New particle formation and its effect on cloud condensationnuclei abundance in the summer Arctic: a case study in theFram Strait and Barents SeaSimonas Kecorius1, Teresa Vogl1,2, Pauli Paasonen3, Janne Lampilahti3, Daniel Rothenberg4, Heike Wex1,Sebastian Zeppenfeld1, Manuela van Pinxteren1, Markus Hartmann1, Silvia Henning1, Xianda Gong1, Andre Welti1,Markku Kulmala3, Frank Stratmann1, Hartmut Herrmann1, and Alfred Wiedensohler1
1Leibniz Institute for Tropospheric Research (TROPOS), 04318 Leipzig, Germany2Institute for Meteorology, University of Leipzig, 04103 Leipzig, Germany3Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland4ClimaCell, Inc., Boston, 02210 Massachusetts, USA
Received: 24 June 2019 – Discussion started: 1 August 2019Revised: 27 September 2019 – Accepted: 11 October 2019 – Published: 27 November 2019
Abstract. In a warming Arctic the increased occurrence ofnew particle formation (NPF) is believed to originate fromthe declining ice coverage during summertime. Understand-ing the physico-chemical properties of newly formed parti-cles, as well as mechanisms that control both particle for-mation and growth in this pristine environment, is importantfor interpreting aerosol–cloud interactions, to which the Arc-tic climate can be highly sensitive. In this investigation, wepresent the analysis of NPF and growth in the high summerArctic. The measurements were made on-board research ves-sel Polarstern during the PS106 Arctic expedition. Four dis-tinctive NPF and subsequent particle growth events were ob-served, during which particle (diameter in a range 10–50 nm)number concentrations increased from background values ofapprox. 40 up to 4000 cm−3. Based on particle formation andgrowth rates, as well as hygroscopicity of nucleation and theAitken mode particles, we distinguished two different typesof NPF events. First, some NPF events were favored by neg-ative ions, resulting in more-hygroscopic nucleation modeparticles and suggesting sulfuric acid as a precursor gas. Sec-ond, other NPF events resulted in less-hygroscopic particles,indicating the influence of organic vapors on particle for-mation and growth. To test the climatic relevance of NPFand its influence on the cloud condensation nuclei (CCN)budget in the Arctic, we applied a zero-dimensional, adia-batic cloud parcel model. At an updraft velocity of 0.1 m s−1,the particle number size distribution (PNSD) generated dur-
ing nucleation processes resulted in an increase in the CCNnumber concentration by a factor of 2 to 5 compared to thebackground CCN concentrations. This result was confirmedby the directly measured CCN number concentrations. Al-though particles did not grow beyond 50 nm in diameter andthe activated fraction of 15–50 nm particles was on averagebelow 10 %, it could be shown that the sheer number of parti-cles produced by the nucleation process is enough to signifi-cantly influence the background CCN number concentration.This implies that NPF can be an important source of CCN inthe Arctic. However, more studies should be conducted in thefuture to understand mechanisms of NPF, sources of precur-sor gases and condensable vapors, as well as the role of theaged nucleation mode particles in Arctic cloud formation.
1 Introduction
Atmospheric new particle formation (NPF), during whichparticles with diameters from 1 to 2 nm are formed, is a phe-nomenon observed in many different environments aroundthe world (Kerminen et al., 2018). Initial steps involved inparticle formation and subsequent growth are usually clus-tering and condensation of both organic and inorganic vapors(Schobesberger et al., 2013). Ions are also known to be in-volved in the nucleation process (e.g., Jokinen et al., 2018). If
Published by Copernicus Publications on behalf of the European Geosciences Union.
14340 S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic
newly formed particles are not lost due to coagulation (Lehti-nen, et al., 2007), and manage to grow to sizes> 50 nm, theycan act as cloud condensation nuclei (CCN, Kerminen et al.,2012). Under the presence of sufficient water vapor, CCNactivate to form cloud droplets (Köhler, 1936). AtmosphericNPF is estimated to be a substantial source of the world’sCCN budget (Merikanto et al., 2009). Thus, in a highly sen-sitive atmosphere such as the Arctic, where CCN numberconcentration is usually low (< 100 cm−3, Mauritsen et al.,2011), NPF may be an important phenomenon controllingthe radiative forcing (Allan et al., 2015; Croft et al., 2016).
During the last decade, Arctic regions have experiencedremarkable changes. Here, the near-surface temperature hasincreased at least 2-fold compared to the Northern Hemi-sphere (a phenomenon known as Arctic amplification, Over-land et al., 2011; Jeffries and Richter-Menge, 2012). In par-allel, a substantial decline in multiyear sea-ice cover (e.g., Biet al., 2018), an increase in sea-ice mean speed and deforma-tion (Rampal et al., 2009), and development of melt ponds(Polashenski et al., 2017) were also observed. Such changesare not only reflected in the dynamics of the Arctic ecosys-tem (Meier et al., 2014), but are also predicted to impact themid-latitude climate (Serreze and Barry, 2011; Cohen et al.,2014; Walsh, 2014).
Recent studies suggest that the amplified warming in theArctic and related changes are a result of a complex inter-action between different feedback mechanisms including pa-rameters such as temperature (Pithan and Mauritsen, 2014),surface albedo (e.g., Screen and Simmonds, 2010; Taylor etal., 2013), water vapor (Graversen and Wang, 2009), cloud(Vavrus, 2004), and the lapse rate (Bintanja et al., 2012). Ad-ditionally, variations in atmospheric and oceanic heat trans-port were also identified as active players in the changingArctic climate (Spielhagen et al., 2011; Alexeev and Jack-son, 2013). Increase in latent heat and moisture transport to-wards the poles may drive the low-cloud formation, and thus,Arctic surface warming (Praetorius et al., 2018). And whilethe mechanisms of lapse rate, surface albedo, temperatureand water vapor feedbacks are rather well understood, thenet cloud feedback still has one of the largest uncertainties(Zhang et al., 2018).
The multi-year analysis of particle number size distribu-tions from the sites around the Arctic Ocean revealed fre-quent new particle formation, occurring either locally or athigher elevations and prevailing mostly during spring andsummer months (Freud et al., 2017; Nguyen et al., 2016;Dall’Osto et al., 2019). In the near future, the frequency ofatmospheric NPF occurrences is expected to increase dueto Arctic sea-ice melt (Dall’Osto, et al., 2017, 2018a, b).This makes measurements of the ultrafine particle physico-chemical properties in the Arctic increasingly valuable ifaerosol–cloud–climate interactions need to be understood(Willis et al., 2018; Abbatt et al., 2019). Contrary to scien-tific interest, such studies in this remote environment still re-main limited, mainly because of logistic challenges in the
region (e.g., Willis et al., 2017; Wendisch et al., 2019). Thefollowing are studies which focus on nucleation mode par-ticles in the Arctic. Wiedensohler et al. (1996) reported theoccurrence of ultrafine particles in the Arctic as a result ofNPF. However, no correlation with potential precursor gaseshas been found. Karl et al. (2012) found that a sulfuric acidnucleation mechanism best explains the observed growth ofnucleation mode particles over the central Arctic Ocean. Inanother study by Karl et al. (2013), marine granular nanogelswere proposed as a novel route to atmospheric nanoparticlesin the high Arctic. Furthermore, NPF in the Arctic region wasassociated with marine biological processes, such as the sea-sonal cycle of the gel-forming phytoplankton by Heintzen-berg et al. (2017). From the results of volatility measure-ments, Giamarelou et al. (2016) have proposed that particlesduring NPF events in the high Arctic exist in the form ofpartly or fully neutralized ammoniated sulfates. Iodine fromcoastal macro algae was detected in the growing particles(Allan et al., 2015; Sipilä et al., 2016), suggesting the iodineas a nucleation precursor. A large body of studies comes fromthe Canadian Arctic region. For example, Croft et al. (2016)showed that ammonia from seabird-colony guano is a keyfactor contributing to bursts of newly formed particles atAlert, Nunavut, Canada. Aerosol particle growth in the Cana-dian Arctic Archipelago during summer was correlated withorganic species, trimethylamine, and methanesulfonic acid(MSA), suggesting an important marine influence (Leaitchet al., 2013; Willis et al., 2016, Abbatt et al., 2019). Park etal. (2017) provided compelling evidence of the contributionof marine biogenic dimethyl sulfide (DMS) to the formationof aerosol particles. Collins et al. (2017) also reported fre-quent ultrafine particle formation and growth in CanadianArctic marine and coastal environments. The authors empha-sized that the low condensation sink, high solar radiation,low sea-ice concentration, and marine microbial processesall contribute to a higher frequency of particle formation andgrowth. Most recently, Tremblay et al. (2019) correlated par-ticle formation and growth events with the melting of the seaice. The authors indicated that besides oxidation of DMS toproduce particle-phase sulfate, other gas-phase organic com-pounds are important for particle growth.
Compared to NPF research in Arctic environments, stud-ies on whether nucleation mode particles (diameter of 20 nm)can act as CCN are even scarcer. Leaitch et al. (2016) inves-tigated effects of 20–100 nm particles on liquid clouds in theclean summertime Arctic and found that particles as smallas 20–50 nm can activate to cloud droplets. This was alsoconfirmed by Burkart et al. (2017b), who found that in theCanadian high Arctic marine boundary layer, newly formedparticles (approx. 30 nm in diameter) are capable of beinginvolved in cloud activation, suggesting that in the pristineenvironment, where cloud radiative forcing is limited by theCCN available (Mauritsen et al., 2011), information aboutaerosol sources is crucial in understanding the link betweensea-ice melt and low-altitude clouds.
S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic 14341
In this investigation, we analyzed four cases of NPF anda subsequent growth from a perspective of particle physical(number concentration, number size distribution, and forma-tion and growth rates) and indirect chemical (hygroscopic-ity) properties. Our main goal here is to test the hypothesisthat NPF and secondary aerosol production can influence theCCN budget in the summertime Arctic. The study is struc-tured as follows. After a short description of materials andmethods in Sect. 2, we proceed by describing each NPF eventseparately (Sect. 3). This includes specification of the meteo-rological conditions during which NPF occurred, characteri-zation of particle formation and growth rates, followed by theobserved hygroscopicity of newly formed particles, and themeasured CCN concentrations during NPF events. We startthe discussion of the results (Sect. 4) with a general overviewof our observations, putting the results into perspective ofother studies. This leads to Sect. 4.1, where we discuss the in-direct evidence of the composition of newly formed particles.Here, we reflect on our observational data as well as varioustechniques to gain information on particle formation mecha-nisms, possible sources of precursor gases, etc. The discus-sion section is closed by investigating the implication of NPFfor cloud formation. This is done by using zero-dimensionalparcel model to examine, whether newly formed and slightlygrown particles can become CCN. Model results are com-pared to measured number concentration of CCN during theNPF events. The main results are summarized at the end ofthe work; general conclusions are also provided.
2 Materials and methods
2.1 Description of observations
The data used in this study were obtained during two legsof an expedition of the German Research Vessel Polarstern(PS 106/1 and PS 106/2): the “Physical feedbacks of Arc-tic boundary layer, Sea ice, Cloud and AerosoL (PASCAL,PS 106/1)” and “Survival of Polar Cod in a Changing Arc-tic Ocean (SiPCA, PS 106/2)” (Macke and Flores, 2018;Wendisch et al., 2019). Both expeditions took place in thevicinity of Svalbard (Norway) from May to July 2017. PAS-CAL was performed in the framework of the ArctiC Am-plification: Climate Relevant Atmospheric and SurfaCe Pro-cesses, and Feedback Mechanisms (AC)3 project and was de-signed to explore cloud properties, aerosol impact on clouds,atmospheric radiation and turbulent-dynamical processes.During the first leg of the trip (PS 106/1, PASCAL), RV Po-larstern reached approx. 82◦ north, where an ice-floe campwas established (5–14 June). The first leg of the expeditionended at Longyearbyen, Svalbard, by 21 June. On 22 June,RV Polarstern left Svalbard for the SiPCA expedition. On thesecond expedition leg aerosol particle measurements wereperformed until 16 July. The cruise track and the ice driftare shown in Fig. 1.
2.2 Measurement setup and equipment
To measure aerosol particle physico-chemical properties, atemperature controlled measurement container, prepared andoperated by the Leibniz Institute for Tropospheric Research,Leipzig, Germany, was installed on the observation deck ofRV Polarstern. The aerosol container was air-conditioned to24 ◦C and the aerosol inlet head was heated to 30 ◦C to en-sure the stability of aerosol instrumentation and prevent ic-ing, respectively. The aerosol inlet was made of 6 m lengthstainless steel tubing, with an inner tube diameter of 40 mm.It was placed on top of the measurement container with anangle of 45 ◦, pointing away from the ship. The aerosol flowin the 6 m long inlet was set to 40 L min−1 (Reynolds number< 2000, laminar flow) to minimize particle losses. Inside thecontainer, an isokinetic splitter was used together with shortand vertical conductive tubes to feed the measurement in-strumentation with an aerosol sample. Aerosol instrumenta-tion (relevant to this study) included a neutral cluster and airion spectrometer (NAIS), a mobility particle size spectrome-ter (MPSS), the Volatility/Hygroscopicity-Tandem Differen-tial Mobility Analyzer (VH-TDMA), and the Cloud Conden-sation Nuclei Counter (CCNC) to measure aerosol particlenumber size distribution, volatility/hygroscopicity propertiesof aerosol particles, and the number concentration of CCN,respectively.
2.2.1 Neutral cluster and air ion spectrometer (NAIS)
A neutral cluster and air ion spectrometer (NAIS, Mirme andMirme 2013) and guidelines by Kulmala et al. (2012) wereused to study early stages of NPF and subsequent growth (in-cluding NPF event classification, formation (J ), and growthrate (GR) calculation). The NAIS measures the number sizedistribution of neutral particles in the diameter range of ap-prox. 2–40 nm and charged particles and clusters in the sizerange of approx. 0.8–40 nm. The instrument is an extendedversion of the air ion spectrometer (Mirme et al., 2007) andutilizes a sample preconditioning section to enable measure-ments of neutrally charged particles. Unipolar corona charg-ers are used for both charging and charge neutralization.Charged particle classification is carried out in the multi-channel differential mobility analyzer (DMA) where 21 in-dividual electrometers are used to record electric current car-ried by the charged particles. Due to high total flow of NAIS(60 L min−1) a dedicated 1.3 m long copper inlet (3.5 cm indiameter) was installed to sample ambient air. Measurementdata were inverted using the v14-lrnd inversion algorithm(Wagner et al., 2016). Particle losses due to diffusion werecorrected before data processing.
2.2.2 Mobility particle size spectrometer (MPSS)
Particle number size distributions (PNSD), in a mobility sizerange from 10 to 800 nm, were measured with a TROPOS-
14342 S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic
Figure 1. Cruise track and particle number concentration (integrated in a size range from 10 to 800 nm) during PASCAL and SiPCAexpeditions. The days which were picked to analyze NPF events and subsequent particle growth are indicated with square boxes. Backwardair mass trajectories (72 h) were calculated using HYSPLIT (Draxler and Rolph, 2012) and are shown by solid (200 m a.s.l) and dotted(2000 m a.s.l) lines corresponding to each NPF event. Ice drift is shown in the insert. Thin blue and black lines are the observed ice edge forJune and July 2017, respectively (Fetterer et al., 2002).
type mobility particle size spectrometer (MPSS, Wieden-sohler et al., 2012). The MPSS consisted of a Hauke-typeDMA (effective length of 28 cm), a condensation parti-cle counter (CPC, model 3772, TSI Inc., USA, flow rate1 L min−1), a closed-loop sheath flow arrangement, and abipolar diffusion charger, ensuring the bipolar charge equi-librium as described in Wiedensohler (1988). The sampleflow rate was controlled by a CPC (1 L min−1) and the sheathflow rate was 5 L min−1. The time resolution of an up-and-down scan was 5 min. Electrical particle mobility distribu-tions were inverted to PNSDs using the inversion algorithmpresented by Pfeifer et al. (2014). The final PNSDs were cor-rected for transmission losses in the sampling lines using themethod of equivalent length and CPC counting efficiencies(Wiedensohler et al., 1997). Sizing accuracy of MPSS wascontrolled using nebulized polystyrene latex spheres (PSL,Thermo Scientific™, Duke Standards™) of 203 nm (Wieden-sohler et al., 2018). High-voltage supply offset calibration,
instrument flows, and tests for leakage were performed on aregular basis (once per week).
Aerosol particle affinity with water and volatility proper-ties (not discussed here) was measured using the TROPOS-type Volatility/Hygroscopicity-Tandem Differential Mobil-ity Analyzer (VH-TDMA, Augustin-Bauditz et al., 2016).The instrument consists of a DMA-1 that selects cho-sen quasi-monodisperse particles, a thermodenuder (notused in this study), an aerosol humidification section thatconditions the particles selected by the DMA-1, and anMPSS-equivalent closed-loop sheath flow unit inside thetemperature-controlled box, which is used to obtain the hy-groscopic growth factor (HGF). The HGF is defined as theratio between the measured particle electrical mobility diam-
S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic 14343
eter at a given RH as measured by the second DMA and theinitially selected dry diameter.
During the whole expedition, two constant aerosol parti-cle sizes, 50 and 150 nm, were selected for the measurementof HGF at a target RH of 90 %. Additionally, HGF of 15,20 and 30 nm size particles were measured during NPF andgrowth events. The system RH, measured by a humidity sen-sor, was periodically calibrated by an automatic calibrationunit, using pure ammonium sulfate. Scans with RH ±2 %from target RH were excluded from data analysis. Sizing ac-curacy, high-voltage supply offset calibration, flow rates, andzero tests were performed regularly (once per week). In gen-eral, recommendations have been followed as described inMassling et al. (2011).
The VH-TDMA data were inverted using a TDMAinv rou-tine (Gysel et al., 2009) to retrieve the probability densityfunctions of GF (GF-PDF). Scans with RH< 20 % were usedto calibrate size offset in the system, as well as to define thewidth of the transfer function (Gysel et al., 2009). The par-ticle hygroscopicity parameter kappa (κ) was derived fromVH-TDMA data following the κ-Köhler theory by Pettersand Kreidenweis (2007):
κ =(
GF3− 1
)·
[1S
exp(
4σsMW
RT ρWDdGF
)− 1
], (1)
where S is the saturation ratio; σs is the surface tension of thesolution; MW is the molecular weight of water; R is the uni-versal gas constant; T is the temperature; ρW is the densityof water; and Dd is the particle dry diameter.
2.2.4 Cloud condensation particle counter (CCNC)
The CCNC (model CCN-100 from Droplet MeasurementTechnologies, Roberts and Nenes, 2005) measured CCNnumber concentrations, subsequently at six different super-saturations (0.1 %, 0.15 %, 0.2 %, 0.3 %, 0.5 % and 1 %),where each supersaturation was sampled for 10 min. Hencean hourly average concentration at each supersaturation isavailable. The instrument was calibrated before and directlyfollowing the campaign using pure ammonium sulfate parti-cles of known sizes, based on the ACTRIS protocol (Gyseland Stratmann, 2013). Only poly-disperse aerosol was sam-pled by CCNC.
2.2.5 Offline chemical analysis
The sampling of aerosol particles was conducted using five-stage low-pressure Berner impactors (Hauke, Austria) witha flow rate of 75 L min−1, which was installed on the top ofthe observation deck facing the ocean at a height of ca. 25 m.Particles were collected in the size ranges 0.05–0.14 µm(stage 1), 0.14–0.42 µm (stage 2), 0.42–1.2 µm (stage 3), 1.2–3.5 µm (stage 4), and 3.5–10 µm (stage 5) aerodynamic par-ticle diameter (50 % cut-off) on aluminum foils as impactionsubstrates, which had been heated at 350 ◦C for at least 2 h to
reduce blank levels prior to sampling. To avoid condensationof atmospheric water on the surface of these aluminum foils,a conditioning unit was mounted between the impactor inletand the sampling unit consisting of a 3 m tube. By heating thesampled air, high relative humidity of the ambient air was re-duced to 75 %–80 % before the collection of the aerosol par-ticles. The temperature difference between the ambient air atthe impactor inlet and the sampled air after the conditioningunit did not exceed 9 K. Thus, the losses due to evaporationof semi-volatile compounds are expected to be minimal.
After sampling, the aluminum foils were stored in alu-minum boxes at −20 ◦C and transported in dry ice to theTROPOS laboratories in Leipzig, Germany. Field blankswere collected by loading the Berner impactor with the alu-minum foils at the sampling site with no air drawn through it.Please note that the sampling time was set to 72 or 144 h (toaccumulate enough particle mass on the filters), thus, it doesnot exclusively comprise the discussed NPF events. For ex-ample, during NPF Event 1, chemical particle compositionwas determined from samples that were collected between29 May (midday) and 1 June (approx. 08:00). During NPFEvent 3, sampling was done between 25 June (11:00) and28 June (09:00).
Particle mass determination was performed by weighingclean (blank) and particle-loaded filters using a microbal-ance UMT-2 (Mettler-Toledo, Switzerland). The concentra-tions of water-soluble methanesulfonic acid (MSA) and inor-ganic compounds relevant to this study (SO2−
4 , NH+4 , Na+)in filtered (0.45 µm syringe) aqueous extracts (50 % of thefilter in 2 mL) were determined using ion chromatography(ICS3000, Dionex, Sunnyvale, CA,USA), as described inMüller et al. (2010). Assuming that the ocean is the majorsource of the measured atmospheric sodium, sea salt sul-fate (ss-sulfate) was calculated from the constant mass ra-tio (SO2−
4 /Na+ = 0.251) in bulk seawater (Galloway et al.,1993; Fomba et al., 2014). Non-sea salt sulfate (nss-sulfate)was calculated by subtracting ss-sulfate from the total sul-fate concentration. The determination of total carbon (TC) asorganic carbon (OC) and elemental carbon (EC) was carriedout by a two-step thermographic method (C-mat 5500, Ströh-lein, Germany) with nondispersive infrared sensor (NDIR)detection as described in Müller et al. (2010). Organic mat-ter (OM) was calculated by considering OM as twice OC(OM= 2×OC) for remote aerosols (Turpin and Lim, 2001).
2.3 Analysis of PNSD measurements
Before NPF event classification, inverted and loss-correctedNAIS and MPSS PNSDs were merged together. For thesmallest particle diameter, from 2 to 10 nm, exclusivelyNAIS data were chosen. This is because the MPSS used inthis study was optimized to operate in a diameter range from10 to 800 nm. The diffusional losses of sub-10 nm particleswere too great to accurately recover the PNSD at initial stepsof nucleation. Contrarily, uncertainties in the NAIS mea-
14344 S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic
sured particle number concentration increases for particle di-ameters larger than 10 nm (Wagner et al., 2016). For thesereasons, PNSDs from both NAIS and MPSS were mergedat 10 nm diameter. No additional treatment (e.g., spline fitto smooth merging distributions) was performed on mergedPNSDs.
Following the protocol by Kulmala et al. (2012), NPFevents were visually identified from the merged PNSDs. Al-though different types of NPFs were recorded (e.g., shortbursts in the smallest particle number as, e.g., described forthe Arctic region by Heintzenberg et al., 2017 and Dall’Ostoet al., 2017), in this work we will only focus on NPF eventswith subsequent particle growth. This type of event includesnot only particle formation, but also includes later particlegrowth lasting for several hours, thus representing a more re-gional phenomenon (Ström et al., 2009). It also allows us tocalculate the GR of the particles, which would not be possi-ble in the case of short nucleation mode particle bursts.
Different methods exist to determine the GR based on themeasured PNSD. For example, maximum-concentration andlog-normal distribution function methods were proposed byKulmala et al. (2012). Tracking regions of PNSD and in-terpreting the change rate of the size-integrated general dy-namic equation methods was suggested by Pichelstorfer etal. (2018). In this work, we used a trial-and-error approachto find the best fit to determine the GR by selectively ap-plying all the mentioned methods for certain NPF cases. Theformation rate of particles of a certain size (J ) was calculatedas described by Kulmala et al. (2012), based on the observedchanges in particle concentrations, GR determined, and par-ticle losses characterized by a coagulation sink (CoagS).
2.4 Adiabatic cloud parcel model
To study the climatic relevance of NPF in the Arctic, we haveused a zero-dimensional, adiabatic cloud parcel model. Thor-ough formulation of the model is given by Rothenberg andWang (2016) and will not be discussed here. Model code isalso freely available at https://pyrcel.readthedocs.io (last ac-cess: 21 August 2019). Shortly, at the initial step, the modelcalculates an equilibrium wet-size distribution from the set ofgiven parameters. This includes the description of the aerosolpopulation and environmental specifications of temperature,pressure, relative humidity, parcel ascending velocity, and theheight of the planetary boundary layer. The aerosol particlepopulation, consisting of two modes, is described by the totalnumber concentration, the geometric mean diameter, and thegeometric standard deviation of the log-normal distribution.The hygroscopicity parameter κ following Petters and Krei-denweis (2007) is used to describe particle chemical compo-sition. The evolutions of the parcel supersaturation, temper-ature, pressure, and liquid/vapor water content are then inte-grated forward in time to describe the thermodynamic evo-lution of an adiabatically lifted, non-entraining parcel. In the
model, the evolution of supersaturation S is
dSdt= α (T ,P )− γ (T ,P )
dwc
dt, (2)
where α and γ are functions depending on temperature andpressure (Leaitch et al., 1986) and wc is the liquid cloud wa-ter mass mixing ratio. Change in temperature is described as
dTdt=−
gV
cp−L
cp
dwv
dt. (3)
V is the updraft velocity, g is gravitational acceleration, cp isthe specific heat of dry air at constant pressure, L is the latentheat of water, and wv is the water vapor mass mixing ratio.Water mass conservation is ensured as vapor condenses intocloud water. Pressure change within the ascending parcel canbe written as
dPdt=−
gV P
RdTv, (4)
where Tv is temperature, Rd – gas constant for dry air. Thechange in cloud water is
dwc
dt=
4πρw
ρa
n∑i=1
Nir2i
G
ri
(S− Seq
). (5)
Here ρa and ρw is the density of air and water, respectively.Ni is a number concentration and ri is radius in a size bin,S is environmental saturation, Seq is the predicted equilib-rium supersaturation under framework described by Pettersand Kreidenweis (2007). G is a growth coefficient, which isa function of both the chemical and physical properties ofparticles.
2.5 Contamination from ship exhaust
During the cruise, ship exhaust occasionally disturbed mea-surements on-board RV Polarstern. This was mostly pro-nounced during the periods when the ship was breaking theice (rapid forward–backward direction change) and/or wasdrifting during sea experiments. Ship exhaust contaminationcan be seen in Fig. 2 contour plots as a sharp increase inparticle number concentrations over the whole particle di-ameter range. The contamination from online measurementswas removed manually. For this, we referred to total parti-cle number concentration observed by separate CPC with 2 stime resolution. The comparison between the total particlenumber concentration and the signal from the single-particlesoot photometer (results are not shown here) confirmed thatthe total CPC indeed is able to observe sharp increase in par-ticle number, which is related to ship exhaust (black carbonparticles).
For offline measurements, an automatic system (to mea-sure relative wind direction) was installed together with ahigh-volume sampler to stop the pumps when the wind di-rection was associated with the pollution sector. A similar
S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic 14345
Figure 2. The NPF events observed during RV Polarstern cruise PS106. The PNSDs from NAIS (negative polarity) and MPSS are shown ascontour plots. The color scale represents particle number concentration as dN/dlogDp. Inside the contour plots, particle number concentra-tion, integrated between two size ranges (10 to 50 and 100 to 800 nm), is shown with dashed and dotted black lines. The presence of coronacharger ions (< 2 nm, Manninen et al., 2011) can also be seen in NAIS data. This artifact was excluded from data analysis. Coagulation andcondensation sinks, meteorological parameters (wind speed and direction, global radiation, temperature, and relative humidity), and forma-tion rates (J ) for each NPF event are shown in the panels below the contour plots. Note: sample contamination by ship exhaust was removedfrom data analysis; however, for better representation of particle growth, the contour plots include all the data (contamination not removed).
approach was used by Huang et al. (2018). The Berner im-pactor, on the other hand, did not have such a system to pre-vent samples from contamination. To avoid measurement ar-tifacts, only samples with the same order of organic carbonas from high-volume samplers were used for data analysisand discussion.
3 Results
During the PS106 cruise, a number of instances wererecorded whereby a total particle number concentration (in-tegrated from MPSS between 10 and 800 nm) steadily in-creased from the background concentrations of several hun-dred to several thousand particles per cm3 (Fig. 1). Aftereliminating the contribution from the ship exhaust (by filter-ing abrupt and short increases in particle number concentra-
tion recorded by a total CPC with 2 s time resolution), thesecases were associated with new particle formation (NPF)events. For further discussion, we have selected four NPFevents with a subsequent particle growth which represent thephenomenon on a regional scale (Ström et al., 2009). To gaininformation about the scale of NPF, additional data of PNSDinformation from the Villum Research Station and ZeppelinMountain Observatory were also taken into account (data forvisual inspection were taken from http://ebas.nilu.no/, lastaccess: 18 March 2019).
The geographic location of the observed NPF events canbe seen in Fig. 1 (indicated with black rectangles and date ofoccurrence), and took place between 78.55 to 81.66◦ N and7.28 to 33.96◦ E. The most intense event (NPF 1) occurredon 1 June 2017, with the total particle number concentra-tion increasing from 100 to more than 4000 particles cm−3.During the NPF event, the lateral distance between RV Po-
14346 S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic
larstern and the nearest coast of Svalbard archipelago was150 km. The least intensive NPF event (NPF 3) was recordedon 26 June, during which the total particle number concen-tration increased from 160 to 700 particles cm−3. Neverthe-less, the subsequent particle growth from 3 to approx. 50 nmlasted for 3 d. All the events that were recorded during June(1, 18, and 26 June) took place in the vicinity of the marginalice zone. The most northern event (NPF 4, 81.6 ◦ north) wasobserved on 2 July 2017. At this time, RV Polarstern was fur-ther away from the marginal ice zone. The average total parti-cle number concentration before the NPF event was approx.100 particles cm−3, which increased to 1400 particles cm−3
during the event.
3.1 Overview of the NPF events
In this paragraph, a detailed overview of the events is pre-sented with the focus on environmental conditions duringwhich NPF occurred, as well as the formation and growthrates of newly formed particles.
3.1.1 NPF 1: 1 June
The first NPF event with a subsequent particle growth wasobserved from around 06:00 onwards on 1 June 2017. RV Po-larstern reached the marginal ice zone at 11:00 and en-tered the pack ice at around 15:00 on 31 May 2017 (notethat all times in this study are given in UTC). This can beseen from the air and water temperature profiles (Fig. 2).The temperature of air and water decreased from approx.+5 to −5 ◦C (air) and −2 ◦C (water). In this area, the icewas broken up by leads, which facilitated the passage ofthe vessel towards the north. Around 20:00 a region withmore densely packed ice was reached, which obstructed themovement of the ship (Nicolaus, 2018). On these occasions,due to frequent reverse–forward ship movement, pollutionhighly affected the measurements on-board (see PNSDs inFig. 1). On 1 June, the vessel could once again pass throughopen leads in the pack ice, allowing for contamination-freescans for the time period from 04:00 to 20:00. During thistime, RV Polarstern moved 26 km (from 80.39◦ N 7.58◦ Eto 80.62◦ N 7.94◦ E) in mostly cloud-free conditions. From18:00 to 20:00, a thin ice cloud was present at over 8 km alti-tude. Also, over a short period from 14:00 to 15:00, intermit-tent low-level liquid clouds were present, which however didnot decrease the global radiation significantly. For a more de-tailed description of local and associated large-scale weatherpatterns during PS106, please refer to Knudsen et al. (2018).
Before the NPF event, the average particle number con-centration in a size range from 10 to 50 nm (PNC10–50) was50 particles cm−3. The particle number concentration in thesize range from 100 to 800 nm (PNC100–800) before the eventdecreased from 150 to as low as 2 particles cm−3. This re-sulted in a sharp decrease in the coagulation sink for 3 nmparticles from 7.6×10−5 to 8.6×10−6 s−1. The condensation
sink also decreased by 1 order of magnitude from 2.2×10−2
to 2.2× 10−3 s−1, creating favorable conditions for particlesto form. The NPF event occurred when the RH was approx.90 % and the particle formation rate peaked when the globalradiation approached the maximum (600 W m−2). The windspeed gradually decreased from an average of 8 m s−1 on31 May 2017 to 5 m s−1 during the NPF event. As a resultof the NPF, the number of ultrafine particles increased by al-most 2 orders of magnitude.
The backward air mass trajectories (calculated for 200 and2000 m above sea level, Draxler and Rolph, 2012) showedpossible intrusion of air from higher altitudes and also thatair was arriving at the ship following the 80 ◦ north latitude,passing over the Prince George Land and northeastern Sval-bard archipelago (Fig. 1). This can be confirmed by the in-crease in ozone concentration at Zeppelin Observatory (Aaset al., 2018; data available from http://ebas.nilu.no/). Follow-ing the NPF event on 1 June, the wind direction graduallychanged from northeast to southwest and brought in a sud-den fog (at 19:00, evident from a steep increase in ambientRH to 100 % and a simultaneous decrease in visibility mea-sured by the vessel’s meteorology station). This can be seenas a sharp increase in both air temperature and RH (to over100 %) causing disruption in the PNSD (onwards from ap-prox. 20:00, 1 June). At the same time, further observationsof the event were corrupted by the local pollution from shipexhaust.
Some parameters describing newly formed particles andions are shown in Table 1. The particle GR in a size rangefrom 3 to 7 nm was 1.2 nm h−1. After the NPF event, sub-sequent particle growth lasted for about 12 h, during whichthe particles were able to grow to approx. 30 nm in diameter(geometric mean diameter). The GR for 1.6 to 3 nm ions wassomewhat more variable – 0.7 for negative and 1.4 nm h−1
for positive ions. Please note that we were not able to cal-culate the positive ion GR in a size range from 1.6 to 3 nm.Instead, the GR for a particle size range 1.6 to 4 nm was cal-culated. The formation rate of 3 nm (J3−) sized neutral par-ticles and negative ions (1.6 nm, J1.6−) was approx. 0.4 and0.045 cm−3 s−1, respectively.
3.1.2 NPF 2: 18 June
On 17 June, the ship was moving southward through packedice area, breaking floes and navigating through polynyas(Nicolaus, 2018). Over the complete day of 17 June, low-level stratocumulus clouds were present, which were brokenup occasionally between 07:00 and 13:00 and between 04:00and 22:00. Between 23:00 on 17 June and 01:00 on 18 June,measured visibility decreased, accompanied by an increase inrelative humidity (RH), indicating fog. This low-level cloudlayer was present until approx. 08:00 on 18 June, whenRV Polarstern left the packed ice, entering the marginal icezone. This resulted in water and air temperature increasesfrom −1.9 ◦C to approx. 2 and 0.5 ◦C above zero, respec-
S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic 14347
Table 1. Calculated parameters for observed NPF events during RV Polarstern cruise 106. The GR is obtained from the NAIS size spectrumusing the methods proposed by Kulmala et al. (2012) and Pichelstorfer et al. (2018). J is the formation rate of 1.6 nm sized positive/negativeion clusters and 3 nm sized particles. Please note that in some instances the size range for GR and J calculations is different (due to measuredPNSD). Nevertheless, we calculated both parameters from the smallest possible particle/ion size range. The value after “±” shows thestandard deviation. Date format: mm/dd.
tively. At the same time, local wind speed decreased from 5to 2 m s−1. During the following hours, until 18:00, no cloudswere present except for a very thin, high ice cloud at 8 kmfrom approx. 11:30 to 12:00. This period of high incidentradiation was only briefly interrupted by a short fog eventfrom 15:00 to 15:30. During this whole time, RV Polarsternmoved through open water, but was always surrounded byfloating ice. Starting at 18:00, a thin low-level cloud layerwas present above the ship, which decreased the global ra-diation significantly. This cloud layer was present until thenext day, 19 June, at approx. 12:00. During 19 June, RV Po-larstern moved through open water and ice along the westerncoast of Spitsbergen (Fig. 1). From approx. 12:30 to 15:00another short cloud-free period led to high global radiation.At 16:00 at approx. 3 km altitude a cloud moved in, decreas-ing the global radiation once again.
The PNC10–50 and PNC100–800 from 17 June prior tothe NPF event were rather stable, with an average valueof approx. 30 cm−3. The corresponding coagulation (for3 nm particles) and condensation sink was 1.2× 10−5 and2.8× 10−3 s−1, respectively. Analysis of backward trajecto-ries showed that since midnight of 17 June, air masses werepassing over the Arctic Ocean and Greenland Sea. Fromthe beginning of 18 June and onwards, air masses were al-ready passing over the northeastern coastal area of Green-land (Fig. 1). The NPF event occurred when the global ra-diation reached its maximum at 570 W m−2 and the RH de-creased to 85 %. During the event, the PNC10–50 increased to3200 cm−3. Particle growth was slightly disturbed by a fogepisode (this can be seen in PNSD and as RH increase to100 % in Fig. 2) at around 15:00 and drizzle at 23:00. Nev-ertheless, the particle growth remained observable until the
evening of 19 June. During this time (after a period of 32 h),newly formed particles grew to approx. 50 nm (geometricmean diameter).
The GRs for particles in the size range from 3 to 7 nm werein a range from 3.6 to 4.9 nm h−1. The GR for 1.6 to 3 nmnegative ions was 2.9 nm h−1, and 4 to 9 nm positive ions3.3 nm h−1. The J3− of particles was approx. 0.35 cm−3 s−1.Formation rate for positive (J1.6−) and negative (J4−) ionswere 0.05 and 0.06 cm−3 s−1, respectively. If compared toEvent 1, it can be seen that despite similar intensity of NPF,particle growth during the second event was approx. 2 timesfaster, and particles were able to grow to larger diameters(30 nm during event 1 versus 50 nm during Event 2).
3.1.3 NPF 3: 26 June
The third, least intensive NPF event occurred during the sec-ond leg of the expedition, 26 June, when RV Polarstern wasat the marginal ice zone, around 200 km east of Svalbard,moving towards the north. Areas dominated by open wa-ter were passed by the vessel, as well as ice-covered water(Nicolaus, 2018). However, the ice was never very denselypacked and the transit of the ship did not require the ice to bebroken. Low-level clouds and fog were present during all of25 to 27 June; on 28 June a short period of cloud-free condi-tions was observed from around 04:00 to 06:00. There weretwo short floe stations, one on 25 June from around 17:00 un-til midnight and the other on 27 June from around midnightto 03:00.
The formation and growth of particles were already ob-served on both 24 and 25 June during less pronounced NPFevents (not shown), when the ship was approx. 100 km southof the Svalbard coast. New particle formation along the east-
14348 S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic
ern coast of Svalbard can be seen in Fig. 1 as an increase intotal particle number concentrations, which were measuredfrom 24 to 28 June, along a distance of more than 600 km.The daily average of PNC10–50 and PNC100–800 from 24 Juneup to the NPF event (26 June) were approx. 600 and 50 cm−3.As a result of NPFs on 24 and 25 June, an interesting pat-tern emerged in 26 June PNSD (Fig. 2). At the beginning of26 June (midnight to 03:00), three distinctive modes with ge-ometric mean diameters of 15, 40, and 150 nm can be seen.The smallest mode at 15 nm is a result of the NPF, whichoccurred on 25 June. These newly formed particles slowlygrew in size and, by 08:00 on 26 June, the mode at 40 nmemerged, which was in turn a result of NPF and subsequentparticle growth observed on 24 June. Larger size particles(150 nm in diameter) seem to exist independently of the NPFevents and were present before, during, and after the NPF on26 June. However, because we were not able to identify parti-cle growth, the NPF events on 24 and 25 June were excludedfrom the result and discussion sections.
The event on 26 June started with relatively calm winds(2 m s−1), which gradually increased to 10 m s−1 over a 3 dperiod (26 to 28 June) with a constant rate of 0.3 m s−1 h−1.The direction of the wind remained stable during the event,with prevailing winds from the south-southwesterly (190 to200◦) direction and stagnant air masses coming from themarginal ice zone. At the beginning of the event, relative hu-midity was at around 87 %, and remained below 95 % dur-ing the whole 3 d period. Air and water temperature duringthe event was approx. −1.5 ◦C. During the described 3 d pe-riod, water temperature remained the same (with some shortepisodes of warmer water), while air temperature steadily in-creased to 0 ◦C. The NPF event occurred with a global radi-ation being at its maximum (200 W m−2); however, this timesolar radiation was at least 2-fold lower than observed dur-ing previous cases. This is due to the presence of a low-levelcloud layer topped at 2 km during the whole day of 26 June.The corresponding coagulation and condensation sink justbefore the event was 2.2× 10−5 and 6.0× 10−3 s−1, respec-tively.
The GR of 3 to 7 nm particles was in a range from 0.5to 0.7 nm h−1. The GRs of negative (1.6 to 3 nm) and pos-itive ions (2 to 6 nm) were accordingly 1.2 and 2.2 nm h−1.Despite the noticeable pollution from ship exhaust, particlegrowth after the NPF event was observed over the period of3 d (Fig. 2). During this time period, particles grew from sev-eral nanometers up to sizes of 50 nm (geometric mean di-ameter). The formation rate of positive (J2−) and negative(J1.6−) ions were 0.03 cm−3 s−1, and the J3− for particleswas approx. 0.08 cm−3 s−1.
3.1.4 NPF 4: 2 July
From midnight of 1 to 4 July, RV Polarstern was movingnorthwards from 81.64◦ N 32.62◦ E to 82.16◦ N 32.87◦ E.This region was mostly ice-covered with some open leads,
through which the vessel could pass without having to breakthe ice. At this time of the expedition, melt ponds were ob-served frequently on the ice floes. On 1 July, there was athick (up to 3 km altitude) low-level cloud layer present until14:00 associated with some snowfall. After 13:00, the cloudbottom height increased steadily; however, some intermittentfog was still present at sea level. A single fogbow was ob-served between 18:20 and 19:00. The fog dissolved at mid-night on 2 July. Almost throughout the entire day of 2 July,no clouds were present except for optically thin cirrus clouds,allowing for high solar irradiation.
On 2 July, RV Polarstern ventured further into the Arc-tic ice, more than 300 km from the coasts of Svalbard andPrince George Land (81.51◦ N, 32.97◦ E). The prevailingwesterly winds were rather stable during a 3 d period (from1 to 4 June) at 6 m s−1. The same was true for water tem-perature, which remained approx. 2 ◦C below zero duringthe whole event period. The air temperature, on the otherhand, varied between −1 and −5 ◦C. The calculated back-ward air mass trajectories indicated that before the midday of1 July, air was coming from the direction of Prince GeorgeLand. The average PNC10–50 and PNC100–800 during thistime was 60 and 70 cm−3, respectively (Fig. 2). From 1 Julyonwards, air masses arriving at RV Polarstern passed closerand closer to the northeastern coast of Greenland, but didnot pass over the land, as was the case for Event 2 (Fig. 1).Effective wet removal of particles by fog could be observedduring the afternoon hours of 1 July, leading to extremelylow particle number concentrations prior to the NPF event.The PNC10–50 and PNC100–800, respectively, decreased to 40and 10 cm−3. The resulting coagulation and condensationsink became 4.5×10−6 and 1.0×10−3 s−1, respectively. TheNPF event started at 08:00 on 2 July at an ambient RH of ap-prox. 90 % and a maximum global radiation of 500 W m−2.In parallel to RV Polarstern measurements, the formationof new particles was also observed at both Villum ResearchStation and Zeppelin Observatory, indicating a regional phe-nomenon.
The particle GR, in a size range from 3 to 7 nm, was0.9 nm h−1. After 40 h of growth, the geometric mean diam-eter of the particles reached 30 nm. The GR of negative ionswas 1.5 nm h−1 (in a size range from 2 to 3 nm). Once again,it has to be noted that, for ions, the GR in the 1.6 to 3 nm sizerange was difficult to obtain. Particle formation rate J3− wasapprox. 0.15 cm−3 s−1. The formation rate of negative ions(J2−) was 0.02 cm−3 s−1. As in the case of Event 1, negativeions seemed to be more prominent than positive ones.
3.2 Particle hygroscopicity during NPF events
The size segregated HGF and hygroscopicity parameter κduring NPF events is presented in Table 2. Diameters andscan times of dry particles that were selected for HGF mea-surements are also indicated in Fig. 2. The HGF scans wereperformed following the growth of freshly formed particles
S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic 14349
from MPSS PNSD measurements. In most of the instancesnewly formed particles grew rather slowly and took between2 and 7 h to grow to diameters of 20–30 nm, when its HGFwas measured. The HGF of 30–50 nm particles was mea-sured between 20 and 40 h after the initial NPF event. De-spite the size of selected dry particles, the measured HGFdistributions were exclusively mono-modal, indicating in-ternal mixture of the aerosol particle. The highest HGF ofnucleation mode particles (15–20 nm) was observed duringEvent 1 and Event 4. The HGF of 20 nm particles duringEvent 1 was measured 7 h after the beginning of the NPF andwas 1.46±0.02 (± standard deviation, SD; κ = 0.41±0.02).At the time of Event 4, HGF of the 15 nm particles was 1.34±0.01 (κ = 0.33± 0.02). The lowest HGF of 20 nm particleswas observed throughout both Event 2 and Event 3 and was1.17 (κ = 0.13± 0.00) and 1.16 (κ = 0.12± 0.02), respec-tively. Hygroscopicity of slightly grown Aitken mode parti-cle (30 to 50 nm) varied from 1.17±0.02 (κ = 0.11±0.00) to1.55±0.01 (κ = 0.38±0.00). In general, the longer the par-ticles aged, the more hygroscopic they became. For example,8 h after the new particles were formed during Event 2, theHGF of 20 nm particles was 1.17± 0.02. After another 15 h,these particles grew to sizes of approx. 30 nm, which HGFincreased to 1.43±0.05 (κ = 0.36±0.08). Interestingly, theHGF of 50 nm particles was somewhat lower, 1.25± 0.01(κ = 0.16± 0.04). Nevertheless, it followed the same pat-tern and with time increased to the values recorded beforethe NPF event.
3.3 Measured CCN concentrations during NPF events
Concentrations of CCN (NCCN) measured during the fourNPF events can be seen in Fig. 3. An increase in NCCN dur-ing these events can be seen across all supersaturations. Todetermine the increase, measured data were fitted, visible aslines in Fig. 3. Data included in the fitting were taken fromtimes on when formation rates of particles were noticeablyincreased (10 % of the maximum signal) and go up to thetime when the NPF event was interrupted by a change in airmass or fog formation. These periods span 10, 39.5, 44.5,and 29 h for NPF events 1 to 4, respectively. Independent ofthe duration of the event, the observed increases in NCCNduring these periods were mostly roughly a factor of 2 forsupersaturations from 0.1 % to 0.5 % and roughly a factor of3 to 6 at 1 %. This larger increase at the highest supersat-uration is related to the fact that the number concentrationsof smaller particles, which are only activated at higher su-persaturations, increased the strongest. During NPF event 2,the increase was somewhat lower, mostly below a factor of2. These measurements clearly show that during NPF eventsnot only new particles are generated, but also that particulatemass is gained on particles of all sizes, increasing their sizeand hence their ability to act as CCN at a given supersatura-tion. A similar observation was made in Antarctica (Herenzet al., 2019), where NPF events with increases in total parti-
Table 2. Hygroscopic growth factor (at 90 % RH) and hygroscop-icity parameter κ during NPF events. Here: time of scans – a timewindow during which hygroscopicity distributions were measured;tJ – approx. time between the observed formation rate maximumand the measurements of HGF. In other words, tJ indicates howlong before/after the NPF events the HGF was measured. For ex-ample, if tJ = 7, the HGF was measured 7 h after the maximum inJ . Negative tJ indicates the measurements of HGF prior NPF event;d0 – selected diameter of dry particles; Nscans – number of scans;SD – standard deviation. Date format: mm/dd.
cle number concentrations from a few hundred to thousandsof particles per cm3 were also accompanied by an increasein NCCN of at least a factor of 2 at all examined supersat-urations. Burkart et al. (2017b) came to similar conclusion.This is in agreement with modeling results by Merikanto etal. (2009), where CCN in Arctic regions were found to al-most exclusively originate from NPF.
3.4 Chemical composition of size-resolved particles
The size-resolved absolute atmospheric concentrations ofammonium, MSA, nss-sulfate, and sea salt (sodium) forthe selected periods versus campaign average are shown inFig. 4. On average, the highest concentrations of nss-sulfate(81 and 70 ng m−3), MSA (18 and 10 ng m−3), and ammo-nium (16 and 8.7 ng m−3) were found in a size range of0.14–0.42 µm (impactor stage 2) and 0.42–1.2 µm (impactorstage 3), respectively. While the concentrations of nss-sulfateand ammonium on the impactor samples from 25 to 28 Junewere comparable to the average values, the impactor samplesfrom 29 May to 1 June stood out with much higher values,especially in the accumulation mode (nss-sulfate: 251 and
14350 S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic
Figure 3. The CCN number concentration measured during NPF events (1 to 4). The lines and corresponding values show the increase inCCN concentrations (prior to NPF versus particles that have grown to the Aitken mode).
295 ng m−3 and ammonium: 34 and 17 ng m−3 in size rangeof 0.14–0.42 and 0.42–1.2 µm, respectively). Also for smallerparticles (size range of 0.05–0.14 µm, stage 1), nss-sulfatewas found at a much higher concentration (35 ng m−3) thanthe average (8.3 ng m−3).
It must also be noted that no action was taken (e.g., sam-pling interrupt-dependent on the specific wind sector) to re-duce ship contamination for the size-segregated aerosol parti-cle measurements. Thus, the contamination from the ship ex-haust cannot be ruled out completely. However, the high con-centrations of biogenic compounds like MSA and the pres-ence of sodium on the aerosol particles suggested a strongmarine influence on the particle composition.
The highest organic matter (OM) mass concentrationswere found at stage 2 (106 ng m−3) and the lowest at stage 5(39 ng m−3). OM mass concentration for the period from 25to 28 June strongly exceeded the average concentration, es-pecially in the accumulation mode (218 and 147 ng m−3 forstages 2 and 3, respectively). For a time period from 29 May
to 1 June the OM mass concentration ranged close to the av-erage values.
Sodium was mainly found at Berner stages 3–5. Thesodium values for the sampling period from 25 to 28 June(Berner stage 4: 49 ng m−3) were quite similar to the averagevalues, while the impactor samples from 29 May to 1 Juneshowed much higher atmospheric concentrations (Bernerstage 4: 386 ng m−3). This agrees well with previous stud-ies, which show that atmospheric sea salt is mostly present insuper-micron particles, while OM contributes strongly to thesubmicron particle composition (e.g., Müller et al., 2010).Previous works also suggest that OM is strongly enrichedduring the bubble bursting process (compared to sea salt),and therefore OM and sea salt are not transferred to the sameextent from seawater to the aerosol particles (Keene et al.,2007; Quinn et al., 2015; Van Pinxteren et al., 2017). It ispossible that increased sodium and OM, observed duringNPF 1, is a result of sea spray; however, due to the low sam-pling time resolution of the Berner cascade impactor, we donot allow ourselves such a conclusion. Moreover, please note
S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic 14351
Figure 4. Size-resolved atmospheric concentrations for ammonium, MSA, nss-sulfate, sodium, and OM for two sampling periods and thewhole campaign average. Stages 1, 2, 3, 4, and 5 correspond to aerodynamic particle diameter ranges of 0.05–0.14, 0.14–0.42, 0.42–1.2,1.2–3.5, and 3.5–10 µm, respectively.
that the increased values of sodium during this time periodmay be related to the ship’s proximity to open water (RV Po-larstern reached the marginal ice zone only on 31 May),while the increase in OM could have happened later (e.g.,1 June) but been included in the same sample. In chemicalsample analysis, we did not find any positive correlation be-tween OM/OC and sodium concerning the different aerosolsize classes. A more detailed chemical characterization of theaerosol particles during the PS 106 cruise will be addressedin a separate publication.
4 Discussion
4.1 General overview
Although NPF events in the high Arctic were reported byseveral studies, there are no observations using the same orequivalent measurement equipment as in this study which areable to observe the dynamic changes in the smallest particles(formation and growth of> 1.6 nm clusters). Because of this,we have also calculated the rate at which new particles appearat larger diameter (10 nm, J10−). The values of so-called ap-parent nucleation rates are more frequently reported in theliterature. For example, in several studies from the Svalbardregion, GRs for 5 to 25 nm particles were reported to be from0.1 to 0.6 nm h−1, but in general ≤ 1.0 nm h−1 (Ström et al.,2009; Giamarelou et al., 2016; Heintzenberg et al., 2017).The corresponding J10− values were in a range from 0.1 to1.4 cm−3 s−1. Nieminen et al. (2018), on the other hand, re-viewed NPF events based on long-term measurements andreported GRs for the Arctic region to be 1.1–1.2 nm h−1 (forthe June–August time period). The reported formation rateswere somewhat lower, 0.008–0.032 cm−3 s−1. In the caseof this study, the GRs for 5–25 nm and J10− values varied
correspondingly from 0.7 to 5.4 nm h−1 and from 0.04 to0.4 cm−3 s−1, respectively. The GR of 5–25 nm size particlesin this study was on average 0.9 nm h−1. The GR of 5–25 nmparticles on 18 June, however, exceeds other NPF events,with the GR being significantly higher, 5.4 nm h−1. Duringthe same event, the J10− was also higher, 0.4 cm−3 s−1. Nev-ertheless, on average, the observed GR and J10− values wereon the same order as reported in other studies from the Arc-tic region (e.g., Asmi et al., 2016; Nieminen et al., 2018).Some studies for similar environmental conditions also ex-ist. Jokinen et al. (2018) provided a comprehensive study onthe particle formation in coastal Antarctica. The growth andformation rates for 3 nm particles were found to be between0.3 and 1.3 nm h−1 and between 0.03 and 0.14 cm−3 s−1. Itwas concluded that ion-induced nucleation of sulfuric acidand ammonia is a major source of secondary aerosol parti-cles in the pristine Antarctic environment. Kyrö et al. (2013)reported formation rates of negative clusters (J1.6−, 0.01 to0.4 cm−3 s−1) measured at the Finnish Antarctic ResearchStation, Aboa, in Dronning Maud Land. In addition, appar-ent nucleation rates of 10 nm particles at Aboa ranged from0.003 to 0.3 cm−3 s−1. In yet another Antarctic study, Welleret al. (2015) reported the average growth and formation rates(in a size range from 3 to 25 nm) to be 0.9 nm h−1 and0.06 cm−3 s−1, respectively. These authors also concludedthat due to an insufficient concentration of low-volatility or-ganic compounds, the particle growth was restricted to thenucleation mode. All of these studies showed some resem-blance to the results observed in our study.
The question is which mechanism drives the nucleationand which are the condensable vapors responsible for the ob-served particle growth in the pristine high-altitude environ-ments. Most recent studies indicate the importance of semi-volatile organics (Willis et al., 2016; Burkart et al., 2017a).
14352 S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic
The subsequent growth of newly formed particles was asso-ciated with organic precursors from meltwater ponds (Kyröet al., 2013), while Weller et al. (2015) speculated that low-volatility organic compounds of marine origin govern thegrowth of newly formed particles in Antarctica. It was alsoshown that in a clean environment, sufficiently high sulfuricacid concentrations (107 molecules cm−3) can fully explainparticle growth (Jokinen et al., 2018). The GRs observed inour study are somewhat similar to those from similar envi-ronments; however, they remain difficult to compare becauseof case-to-case variability.
Insights on the chemical composition of nucleation modeparticles and the climatic relevance of NPF can be drawnfrom the hygroscopicity measurements either at water va-por sub-saturation (measurements of HGF) or supersatura-tion (measurements of the number of CCN). While κ is a pa-rameter that is independent of experimental conditions, HGFstill depends on the dry particle size and RH for which itwas determined. Still, for the Arctic more data are availablefor HGF, so that we will use this parameter for comparisonwith the literature in the following. Zhou et al. (2001) mea-sured the HGF during the Arctic Ocean Expedition 1996. TheHGF of nucleation mode particles (just after a NPF event,dry diameters of 15) was 1.38. The HGF of 35 nm particleswas 1.56. After some time, the particles that grew to sizesof 50 nm were found to be less hygroscopic (HGF of 1.05).It was suggested that these particles were produced at thesea surface and not in the free troposphere. However, the au-thors could not derive the composition of those nucleationmode particles. Park et al. (2014) reported HGF values of50 nm particles during enhanced number concentration of theAitken mode to be 1.46. Sulfate and biogenic volatile organicspecies were identified to contribute to the Aitken mode par-ticle formation. Compared to our measured HGF of 15 and20 nm particles, we can see that during events 1 and 4 val-ues agree reasonably well with previously measured particlehygroscopicity. The HGF values of nucleation mode parti-cles during events 2 and 3, on the other hand, are signifi-cantly lower. The hygroscopicity of the Aitken mode parti-cles, measured during Event 4 was almost identical to thatnoted by Park et al. (2014). On the other instances, for exam-ple Event 2, the HGF of the Aitken mode particles was lower(1.33 versus 1.46) than previously reported values. It clearlyindicates that different condensable vapors were driving thegrowth of newly formed particles into sizes of 30 to 50 nm.
Based on particle hygroscopicity, formation and growthrates of positive/negative ions and neutral clusters, and of-fline chemical analysis, our observed NPF events representtwo different cases: (1) more hygroscopic particle forma-tion favored by negative ions, events 1 and 4 (1 June and2 July, respectively); and (2) relatively low hygroscopicityparticle formation during events 2 and 3 (18 and 26 June, re-spectively), suggesting the presence of condensable organicsin particle growth. Further, we would like to discuss event-specific particle growth/formation rates and hygroscopicity
with respect to formation mechanism and condensable va-pors.
4.2 Indirect evidence of the composition of newlyformed particles
4.2.1 NPF 1 and 4
Occurrences of nucleation mode particles in the summerArctic were associated with intrusion from higher altitudesand new particle production in upper layers of the marineboundary layer (MBL, e.g., Wiedensohler et al., 1996). Itis possible that the NPF precursors can be brought fromeither open ocean or anthropogenic continental sources byair masses. Coupled with low condensation and a coagula-tion sink and with plentiful global radiation, it creates favor-able conditions for new particles to be formed. However, inall of our observed NPF cases the particle formation startedfrom nucleation of 1–2 nm clusters, suggesting that the NPFtook place right at the sea level, rather than in upper layersof the MBL. In this study, unfortunately neither the high-resolution online chemical composition of aerosol particlesnor relevant gases (e.g., SO2, O3) were directly measured on-board RV Polarstern. To gain some insights into the chem-ical composition of newly formed and slightly grown par-ticles, as well as precursor gases, we used measured parti-cle physico-chemical properties (e.g., hygroscopicity, growthrate) as well as satellite imagery.
It is known that Arctic phytoplankton contributes to theproduction of dimethyl sulfide (DMS), which is the mainsource of biogenic sulfur (Stefels et al., 2007; Levasseur,2013, and reference therein). Released into the atmosphere,DMS can be involved in NPF through oxidation and creationof sulfuric acid (H2SO4) (Kulmala et al., 2001; Park et al.,2017). In a study by Nguyen et al. (2016), NPF and particlegrowth at Station Nord, Greenland, were found to be linkedto O3, most likely through creation of a hydroxyl (OH) radi-cal and oxidation of sulfur dioxide (SO2) and volatile organiccompounds. The satellite-derived chlorophyll-a mass con-centration in surface seawater, as an indicator of phytoplank-ton biomass (Becagli et al., 2016), can be seen in Fig. 5 (left).It is evident that during all NPF events RV Polarstern wasin close proximity to an area of increased biological activityin the Arctic Ocean. During Event 1, we also observed largeice-attached mats of the Melosira arctica (Fig. 5), which sug-gests the presence of DMS (Levasseur, 2013). It can also beseen from Fig. 5 that sea-ice retreat is somewhat linked to in-crease in chlorophyll-a mass concentration in surface seawa-ter. For example, on 26 June some ice coverage in the south-ern part of Prince George Land can still be visible, while on2 July it is all gone, replaced by biological activity. This ismost likely because the ice edge provides increased stabilityfrom the meltwater, which facilitates the seasonal productionof phytoplankton (Conover and Huntley, 1991).
S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic 14353
Figure 5. Sea-ice concentration (white – 100 %, dark blue – 1 %; from NASA Worldview; Maslanik and Stroeve, 1999) and chlorophyll-asurface concentration (taken from http://marine.copernicus.eu, last access: 29 April 2019) during NPF events (a, b, d, e). On the right – theice alga and diatom Melosira arctica (c, f) observed from the ship deck during NPF Event 1. RV Polarstern track and location during theNPF event are indicated by the red line and black circle, respectively. Orange lines mark the 72 h backward air mass trajectory at 200 m a.s.l.
An interesting feature was observed with respect to forma-tion rates and the number size distributions of positive andnegative ions during events 1 and 4 (Fig. 2; see also Fig. S1in the Supplement). Firstly, it seems that the formation ofions occurred before that of neutral particles. The peak ionformation rate was observed approx. half an hour prior tothe formation of neutral particles. Although not in the polarregions, similar behavior was noticed in several other stud-ies, suggesting the importance of ions in NPF events (Man-ninen et al., 2010; Jayaratne et al., 2016). The role of ionsin NPF was investigated in both laboratory and field studies(e.g., Wagner et al., 2017; Jokinen et al., 2018). It was shownthat ions enhance the nucleation and condensation of the va-por molecules by stabilizing the molecular clusters and/orare involved in charged cluster neutralization via recombina-tion with oppositely charged clusters. The second interestingfeature that was observed only during events 1 and 4 wasthe absence of the smallest (< 1.6 nm) positive ions. Neg-atively charged ions seemed to be involved in the particleformation more favorably than the positive ones. This wasalso observed in previous studies (e.g., Hirsikko et al., 2007;Asmi et al., 2010; Jokinen et al., 2018) and was associatedwith sulfuric-acid nucleation. Although H2SO4 concentra-tions were not determined directly, the presence of negative
clusters suggests that in the case of events 1 and 4, sulfuricacid was somewhat involved in observed NPF, too.
From previous studies, it was shown that H2SO4 concen-tration of 107 molecules cm−3 are sufficient to explain theobserved new particle GRs in coastal Antarctica (Jokinenet al., 2018). In our case, the hypothesis was tested thatH2SO4 was involved in NPF events 1 and 4 by using thelook-up tables from an ion-mediated nucleation model forthe H2SO4–H2O binary system (Yu, 2010). At a given tem-perature (TEvent1 = 268.8 K; TEvent4 = 268.4 K), relative hu-midity (RHEvent1 = 96.3 %; RHEvent4 = 96.23 %), and sur-face area concentration of pre-existing particles (SEvent1 =
2.9 µm2 cm−3; SEvent4 = 0.5 µm2 cm−3), and assumed ion-ization rate (Q= 2 ion-pairs cm−3 s−1) – the correspond-ing H2SO4 concentration was calculated to be approx.106 molecules cm−3. If compared to a study from Antarc-tica (Jokinen et al., 2018) or laboratory studies by Dunne etal. (2016) from the CERN CLOUD (Cosmics Leaving Out-door Droplets) chamber, our calculated H2SO4 concentrationis 10 to 30 times lower than that from previous studies. Onthe other hand, the results of this study are in agreement witha study by Ehn et al. (2007), who studied the relationship be-tween particle hygroscopicity and sulfuric acid concentrationin boreal forest. The authors reported that the concentrationof H2SO4, corresponding to 15 and 20 nm particle HGFs of
14354 S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic
1.34 and 1.46, was in a range of 107 molecules cm−3. Never-theless, there were numerous instances when the same hygro-scopic growth was also observed at lower H2SO4 concentra-tions (< 107). Moreover, both in the Arctic and Antarctica,H2SO4 concentrations of 106 molecules cm−3 were associ-ated with NPF by Croft et al. (2016) and Kyrö et al. (2013),respectively.
The fraction of the particle growth that can be explained bysulfuric acid can be found from the comparison of observedversus predicted particle growths. From Vakkari et al. (2015),the particle growth due to sulfuric acid can be found from therelation
GRcalc =CH2SO4
A, (6)
where coefficient A is equal to 1.58× 107, 1.99× 107, and2.28×107 for particle growth in the size range from 1.5 to 3,3 to 7, and 7 to 20 nm, respectively. Using our estimated con-centration of H2SO4 we found that growth (in a size rangefrom 1.5 to 3 nm) due to sulfuric acid alone accounts onlyfrom 4 % to 10 % of the observed growth during Event 4 and1, respectively. The contribution to particle growth in a sizerange from 3 to 20 nm gets even lower, 4 %–5 %. Our val-ues are somewhat comparable to those observed in Antarc-tica (Kyrö et al., 2013). It suggests that besides sulfuric acid,other vapors have to be present to reach the observed particlegrowth. From offline chemical analysis, we see that duringEvent 1, ammonium and nss-sulfate in accumulation and theAitken mode particles were somewhat higher than campaignaverage (Fig. 4). Some studies (e.g., Croft et al., 2016; Köll-ner et al., 2017) identified that certain nitrogen-containingspecies such as ammonia and amines are linked to particlegrowth in the Arctic region. To test this, we investigate theformation rate of critical clusters using a parametrization ofthe ternary H2SO4–NH3–H2O system, presented by Napariet al. (2002). That is, we adjust the concentrations of H2SO4and NH3 until we get the formation rate close to that of ob-served value. The estimated concentrations of H2SO4 andNH3 varied from 1×104 to 5×106 cm−3 and 0.1 to 100 ppt,respectively (see Supplement). According to Wentworth etal. (2016), such concentrations of NH3 can be indeed foundin the Arctic region. There is evidence that H2SO4–NH3–H2O clusters are only partly neutralized under atmosphericconditions (e.g., Kurtén et al., 2007; Schobesberger et al.,2015). On the other hand, Asmi et al. (2010) reported thatAitken mode particles are somewhat more neutralized. Now,if we assume that the newly formed particles were partlyneutralized by ammonia (as suggested by Giamarelou et al.,2016), we would expect particle hygroscopicity to be close tothat of ammoniated sulfates. However, our observed HGFsof 20 and 30 nm particles during both events were some-what lower (e.g., 1.46 versus 1.64, Asmi et al., 2010). Similarhygroscopicity of ultrafine particles (HGF= 1.38 for 15 nmparticles) in the Arctic was observed by Zhou et al. (2001).However, the authors excluded the water–sulfuric acid nu-
cleation as a source of such particles because < 50 nm par-ticles did not appear to be composed of either sulfuric acidor ammonium sulfate. Kim et al. (2016) measured the hygro-scopicity of nanoparticles produced from homogeneous nu-cleation in the CLOUD experiment. If compared to CLOUDexperiment results, the measured hygroscopicity of 20 nmparticles during Event 1 was closest to the results of experi-ment, during which sulfuric acid and dimethylamine (DMA)concentrations were 7.6× 106 molecules cm−3 and 23.8 ppt,respectively. With that being said, experiments with sulfu-ric acid (15.1× 106 molecules cm−3) and organics producedfrom α-pinene ozonolysis (420 ppt) resulted in 15 nm parti-cles with HGF= 1.33, which is identical to those observedduring Event 4.
To conclude, one can only assume that during events 1 and4, the NPF was initiated by sulfuric acid. Although the in-volvement of ammonia in new particle formation is possi-ble, it cannot be proven by this work. The organics of marineorigin could have been involved in particle growth to someextent. However, low (compared to the campaign average)organic matter concentrations, observed by offline chemicalanalysis, contradict the aforesaid conclusion. The hypothesisthat NPF is driven by sulfuric acid can be supported by theresults of neutral cluster and ion number size distribution andhygroscopicity measurements of nucleation mode particles.
4.2.2 NPF 2 and 3
Following the same line of thought as in the previous sec-tion, we investigate to what extent sulfuric acid may havebeen involved in the NPF and growth during events 2 and 3.From satellite imagery of chlorophyll a (Fig. 5), we can seethat RV Polarstern remained in close proximity to somewhatdecreased but still present biological activity in the ArcticOcean. In addition to that, some depletion in sea-ice coverclose to Greenland as well as an increase in biological activ-ity south of Svalbard were also observed (Fig. 5). Thus, it issafe to say that air masses arriving at RV Polarstern werepassing over regions which are a potential source of bothDMS and organics of marine origin. Assuming a H2SO4–H2O binary system, the H2SO4 concentrations correspond-ing to formation rates of those observed for events 2 and 3were 15 % to 50 % higher, compared to events 1 and 4. Thisis mainly because during events 2 and 3 both the condensa-tion sink and temperature were higher too. Only between 1 %and 3 % of observed particle growth during Event 2 can beexplained by H2SO4 alone. This fraction is somewhat higheron Event 3 (6 %–9 %). At the initial states of nucleation modeparticle growth, particle hygroscopicity on both events wasrather low (HGF between 1.16 and 1.18). Such low hygro-scopic particle growth, coupled with a rather rapid increasein size (Event 2, from 3 to 20 nm, GR= 4.2 nm h−1), sug-gests that in these events the organics must have played amuch bigger role during initial particle growth than duringevents 1 and 4. The observed particle hygroscopicity agrees
S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic 14355
rather well with less-hygroscopic particle values reported byZhou et al. (2001). During Event 2, particle hygroscopicitydid not change much when particles from nucleation modegrew into the Aitken mode, with HGF remaining between1.16 and 1.18. Only after approx. 30 h after the new parti-cles were created did they grow to a diameter of 50 nm withslightly increased hygroscopicity, HGF= 1.33. Contrarily, inEvent 3 the HGF of 50 nm particles (after approx. 40 h af-ter the nucleation) reached a value of 1.55. It is expectedthat with time newly formed particle hygroscopicity will in-crease due to the process known as aging. From smog cham-ber experiments, Tritscher et al. (2011) showed that organicaerosol photochemical aging increases the particle hygro-scopicity mainly due to O3 induced condensation of organicmolecules onto particles. The rate at which particle hygro-scopicity parameter κ increases can be calculated from thechange in κ over the time period (1κ/1t). We found thatduring events 2 and 3 κ changed with the rates of 0.0027 and0.0067 h−1, respectively. These values are surprisingly closeto those observed by Tritscher et al. (2011), further support-ing the evidence of organics participating in our observedparticle growth.
Using our calculated formation rates (0.06 and0.026 cm−3 s−1 during events 2 and 3, respec-tively) and sulfuric acid values from previous studies(5× 106 molecules cm−3, Croft et al., 2016) as a guideline,we calculate the extremely low-volatility organic com-pound concentration from the parameterization of particleformation rate as a function of sulfuric acid and EL-VOCconcentration (Riccobono et al., 2014):
J = 3.27× 10−21 cm−6 s−1× [H2SO4]2
× (EL-VOC) . (7)
The resulting EL-VOC concentration for Event 2 was foundto be approx. 8.0× 106 molecules cm−3. This is 40 timeshigher than what is expected from monoterpene air–sea fluxin the Arctic Ocean (Croft et al., 2016). On the other hand,during Event 3, the estimated concentration of EL-VOC wasin pair with results published by the same authors. The ques-tion is where the EL-VOC comes from. Kyrö et al. (2013)showed that NPF can be a result of precursor vapor emissionfrom meltwater ponds. In Fig. 5, we can see that air massesduring Event 2 are arriving from the coast of Greenland,with a pronounced sea-ice index change, indicating ice re-treat. Moreover, measurements of PNSD at Villum ResearchStation also indicated the occurrence of NPF. However, it re-mains unclear whether the ice and biological activity devel-opment at the coast of Greenland could have produced theorganic vapors that participated in NPF observed at RV Po-larstern. Yet another source of condensable organic vaporcould be the aged phytoplankton blooms, presented as irreg-ularities in chlorophyll-a spatial distribution, at the marginalice zone, close to the research vessel.
Atmospheric particulate methanesulfonic acid (MSA) andnon-sea salt sulfate (nss-sulfate) are considered to be ox-idation end products of DMS, which is released as a gas
during biogenic processes and indicates the formation ofsecondary aerosol with biogenic origin (Leck et al., 2002;Miyazaki et al., 2010). MSA was shown to be involved innucleation mode particle growth in the Arctic by Willis etal. (2016). The authors found that MSA and condensableorganic species, originating from marine-derived biogenicvolatile organic compounds, drive particle growth in a shal-low marine inversion layer. Organic matter in Arctic submi-cron particles was found to be of both continental and bio-genic marine origins (Kerminen et al., 1997; Chang et al.,2011). Orellana et al. (2011) showed that submicron OM canbe composed of phytoplankton exudates in form of marinehydrogels. If we look at offline chemical analysis of aerosolsamples, OM was found on all impactor stages, especiallyon the submicron particles between 0.14 and 1.2 µm. Whilesubmicron particles of the impactor samples for Episode 1were mainly dominated by ammonium and nss-sulfate (seeFig. 4), higher concentrations of OM (together with MSA)were found for the sampling period between 25 and 28 June.These results corresponded to the observed differences be-tween particle hygroscopicity during events 1 and 3.
To summarize, the rapid particle growth (Event 2) andthe low but steadily increasing hygroscopicity (events 2 and3) suggest that organics must have been involved in bothNPF and subsequent particle growth. Although our observedresults agree with previously made conclusions that parti-cle growth in the Arctic is largely via organic condensation(Burkart et al., 2017a), due to a lack of measurements, wecannot specify which organic species may/or may not havebeen involved in these processes. We also cannot excludeeither the role of iodine (Allan et al., 2015) in the initialsteps of NPF or other pathways for initial particle growth(e.g., aminium salts; Smith et al., 2010). In the future, mea-surements of the chemical composition of naturally chargedair ions and ion clusters and low-volatility aerosol precursorgases would greatly improve our understanding of NPF pro-cesses and particle growth in the Arctic.
4.3 Implication for CCN abundance
In the last section of this work, the climatic relevance of thenewly formed particles in the Arctic is discussed. In severalstudies (e.g., Allan et al., 2015; Willis et al., 2016; Burkartet al., 2017b) it was reported that nucleated particles in theArctic atmosphere rarely grow beyond the Aitken mode. Itis the result of low organic vapor/precursor gas concentra-tions involved in NPF and subsequent growth, as well as par-ticle lifetime (particles being scavenged by fog or precipita-tion, Karl et al., 2012). These findings are also comparableto those from Antarctica. Weller et al. (2015) reported thatparticle growth is governed by the deficit or availability oflow-volatility organic compounds of marine origin and drewthe conclusion that particles do not grow to a diameter rangerelevant for action as CCN. On the other hand, some stud-ies both from Arctic and Antarctica proved that particles do
14356 S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic
not have to grow beyond 50–60 nm in diameter to be ableto act as CCN (Kyrö et al., 2013; Croft et al., 2016; Leaitchet al., 2016). This is because in the pristine Arctic environ-ment the absence of larger particles may lower water uptake,which will increase supersaturation, enabling cloud water tocondense on smaller particles (Leaitch et al., 2016).
To examine to which degree NPF may influence the CCNnuclei budget in the Arctic, we used an adiabatic non-entraining cloud parcel model (described in Sect. 2.4). Allthe initial parameters and simulation results can be foundin Table 3. The change in CCN number was calculated fortwo different updraft wind velocities, 0.1 and 3.2 m s−1, rep-resenting the 75th percentile and maximum value, respec-tively. The measurements of vertical wind velocity was per-formed during the ice-drift station, as described by Egerer etal. (2019). We define the CCN number concentration (NCCN)increase due to particles created in the nucleation process as
increase in NCCN =
(NCCN,bp+NCCN,NPF
)NCCN,bp
, (8)
where (NCCN,bp+NCCN,NPF) is the number concentration ofCCN resulting from the particles created in NPF event (cal-culated from bi-modal PNSD using parcel model; see Table 3for simulation parameters) and NCCN,bp is the CCN num-ber concentration resulting entirely from accumulation modeparticles present during the NPF event (the newly formedparticle mode is suppressed in parcel simulation). For amore detailed discussion about the CCN increase calculation,please refer to the Supplement. It can be seen that for mostof the cases (when RH> 90 %), the CCN number concentra-tions increased by a factor of 2 to 5 (at upward wind veloc-ities of 0.1 m s−1) and 4 to 32 (at upward wind velocities of3.2 m s−1). Although the activated number fraction in a sizerange from 15 to 20 nm was rather low (1.5 %–4 %), the highnumber of nucleation mode particles resulted in a noticeableincrease in total CCN. The CCN fraction was higher (30 %–50 %) when 3.2 m s−1 updraft wind speed was assumed. Forthe Aitken mode particles, CCN fraction was approx. 12 %and 80 % for updraft wind speeds of 0.1 and 3.2 m s−1, re-spectively. In some cases, the particles did not activate toCCN. This is because activation supersaturation was notreached during the parcel updraft. The maximum supersat-uration achieved with an updraft velocity of 0.1 m s−1 was0.17 %. The updraft velocity of 3.2 m s−1 would represent,although rare, however, a not unlikely situation when super-saturations of 0.9 % can be reached. It can be anticipatedthat an even higher fraction of CCN may result from nucle-ation mode particles when higher supersaturation values arereached. Measurements of CCN number concentration on-board RV Polarstern corroborate the results obtained by ourmodeling efforts, which all are in good agreement with pre-vious works. For example, Croft et al. (2016) reported max-imum supersaturation in the Arctic region of 0.15 %–0.25 %for the updraft speed of 0.1 m s−1. From a comprehensive
study on the ultrafine particle effects on liquid clouds in theclean summertime Arctic, Leaitch et al. (2016) determinedthe supersaturation for low- and high-altitude clouds to beapprox. 0.3 % and 0.6 %, respectively. In the Arctic environ-ment with the lack of aerosol particles upon which cloudsmay form, even a small increase in aerosol loading can leadto cloud formation and thus influence the ice-covered Arcticsurface (Mauritsen et al., 2011). From our results, we con-clude that NPF in the Arctic can play a significant role indetermining the future changes in this pristine and remoteenvironment.
5 Summary and conclusion
Aerosol particle physico-chemical properties were deter-mined in the summer Arctic on-board research vessel (RV)Polarstern from 26 May to 16 July 2017 as a part of thePASCAL/SiPCA campaign. Here, regional NPF events areanalyzed and put into prospective of producing the CCN.From the measurements of neutral cluster and air ion num-ber size distributions, it can be concluded that new particleswere formed within the marine boundary layer and not mixeddown from aloft. Therefore, the majority of particles in a sizerange up to 50 nm in diameter can be related to secondaryaerosol production rather than primary emissions. Two dif-ferent types of NPF were distinguished: (a) NPF favored bynegative ions, and more-hygroscopic nucleation mode parti-cles; and (b) NPF with subsequent rapid growth (Event 2),resulting in less-hygroscopic particles. From analysis of par-ticle formation and growth rates, as well as the hygroscop-icity of slightly grown particles, it seems that sulfuric acid–water ion-mediated nucleation is an acceptable mechanismexplaining the observed NPF during events 1 and 4. Mean-while, low particle hygroscopicity and rapid growth suggestthat condensable organics were somewhat involved in parti-cle growth during events 2 and 3. Although the imagery fromsatellites confirms the biological activity as a possible sourceof marine sulfur and organics, due to the lack of appropriatemeasurements, we cannot provide quantitative informationabout the extent to which these precursor gases may havebeen involved in the observed particle formation and growth.For the same matter, we also cannot exclude other species(e.g., iodine) participating in NPF. To answer these questions,high temporal resolution measurements of nucleation and theAitken mode particle chemical composition after the NPF arenecessary, which remain a topic for future research.
After the nucleation, in 12 to 56 h newly formed particlesgrew to the Aitken mode sizes (approx. 30–50 nm). We havetraced particle growth and measured particle hygroscopicityfor dry diameters of 15, 20, 30, and 50 nm. Here, one of ourmain objectives was to test whether particles created in theArctic marine boundary layer can act as CCN. To accomplishthis task we have used a zero-dimensional, adiabatic cloudparcel model. Measured particle physico-chemical properties
S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic 14357
Table 3. Input parameters and the results from parcel model (Rothenberg and Wang, 2016). Here: P – pressure (Pascal), T – temperature(Kelvin), RH – relative humidity (%), GMD – geometric mean diameter of two modes fitted to PNSD (in nanometers); N – number concen-tration of particles in the mode (in particles per cubic centimeter), κ – hygroscopicity parameter kappa (derived for particle sizes indicated inbracket), σ – the shape parameter (standard deviation of the log of the distribution), NCCN,0.1, and NCCN,3.2 – the number concentration ofCCN at two different vertical wind velocities, 0.1 and 3.2 m s−1. Note: κ for specific GMDs was adopted from the nearest value of measured15, 20, 30, 50, and 150 nm particle hygroscopicity. For example, hygroscopicity of 20 nm particles was used as an input value for the GMDof 16 nm mode particles. Date format: yyyy-mm-dd.
Time P T RH GMD N κ σ NCCN,0.1 NCCN,3.2(Pa) (K) (%) (nm) (cm−3) (cm−3) (cm−3)
and ambient information (relative humidity, pressure, tem-perature) were used to simulate particle population activationto cloud droplets at two different updraft velocities of 0.1 and3.2 m s−1. Simulation results showed that although the acti-vated fractions of nucleation mode particles were below 5 %at an updraft wind velocity of 0.1 m s−1, background CCNnumber concentration increased by up to a factor of 5. TheAitken mode particle activation was somewhat higher, ap-prox. 12 %. Such an increase in CCN number concentrationswas also confirmed by direct measurements for supersatura-tions from 0.1 % to 1 % on-board RV Polarstern. Our find-ings support previous observations suggesting that in a pris-tine Arctic environment particles do not have to grow to sizesabove 50 nm to act as CCN. We conclude that in a changingArctic, NPF can be an important source of CCN. New par-ticle formation and the Aitken mode particles’ ability to be-come CCN require more in-depth studies with the focus on
mechanisms of NPF, chemical composition of the precursorgases and condensable vapors, as well as the identification oftheir sources and impact on Arctic clouds.
Data availability. Processed and raw data are available on requestfrom the corresponding author.
Supplement. The supplement related to this article is available on-line at: https://doi.org/10.5194/acp-19-14339-2019-supplement.
Author contributions. SK operated aerosol instrumentation on-board RV Polarstern, evaluated data, and wrote the manuscript. TVoperated aerosol instrumentation on-board RV Polarstern and con-tributed to the manuscript writing. PP, JL, and MK contributed tothe NAIS data evaluation, discussion, and manuscript writing. DR
14358 S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic
contributed to the simulation of CCN. HW contributed to the writ-ing of the manuscript. SZ and MvP collected samples for chemicalanalysis and contributed to the writing of the manuscript. MH oper-ated the CCNC on-board RV Polarstern and evaluated CCNC data.XG and AWe operated CCNC on-board RV Polarstern. SH cali-brated the CCNC prior measurement campaign. FS, HH, and AWiparticipated in fund raising for the measurement campaign.
Competing interests. The authors declare that they have no conflictof interest.
Special issue statement. This article is part of the specialissue “Arctic mixed-phase clouds as studied during theACLOUD/PASCAL campaigns in the framework of (AC)3
(ACP/AMT inter-journal SI)”. It is not associated with a confer-ence.
Acknowledgements. We gratefully acknowledge the funding bythe Deutsche Forschungsgemeinschaft (DFG, German ResearchFoundation) – Projektnummer 268020496 – TRR 172, withinthe Transregional Collaborative Research Center “ArctiC Ampli-fication: Climate Relevant Atmospheric and SurfaCe Processes,and Feedback Mechanisms (AC)3, as well as funding of RV Po-larstern cruise PS106 (expedition grant number AWI-PS-106-00)by AWI. The authors would also like to acknowledge a num-ber of people who were involved in this work. We acknowledgethe discussions and support (H2SO4–H2O nucleation look-up ta-bles) by Fangqun Yu (UAlbany). We also thank Sebastian Ehrhart(MPIC), Joachim Curtius (IAU), Steffen Münch (ETHZ), andAndreas Kürten (IAU) for the discussions concerning sulfuricacid–water nucleation, Ella-Maria Duplissy, Veli-Matti Kerminen,Jenni Kontkanen, Stephany N. Buenrostro Mazon from HelsinkiUniversity for their time, valuable suggestions, and discussions, Ul-rike Egerer for providing the updraft wind velocities during theice-drift station, Hannes Griesche, Ronny Engelmann, and Mar-tin Radenz for providing ship-based remote sensing data to char-acterize the cloud situations during the selected events, Peter Gege(DLR), Svenja Kohnemann (UniTrier), and Marcel Nicolaus (AWI)for sharing the ship-deck photos, Andreas Macke (TROPOS) andHauke Flores (AWI), Chief Scientists of PS106 cruise, for the at-titude and phenomenal attention to all our requests regarding sci-entific activities on-board RV Polarstern and on the ice, and fi-nally, the RV Polarstern crew, staff members, numerous scien-tists, and polar bear guards and watchers, who made the expedi-tion not only exceptional, but also a safe experience. Villum Re-search Station, Robert Lange, Andreas Massling, Henrik Skov, andNiels Bohse Hendriksen are acknowledged for providing PNSDdata. We acknowledge Hartmut and Andrea Haudek for buildingthe conditioning system for both the aerosol inlet and the Bernerimpactor for these Arctic environmental conditions. Maik Merkeland Rene Rabe were a huge technical support for setting up themeasurement container and Berner impactors. Susanne Fuchs per-formed the ion chromatography analysis and Anke Rödger theOC/EC thermographic analysis. We also acknowledge the use ofimagery from the NASA Worldview application (https://worldview.earthdata.nasa.gov, last access: 3 June 2019), part of the NASA
Earth Observing System Data and Information System (EOSDIS).Also, this study has been conducted using E.U. Copernicus MarineService Information (Arctic Chlorophyll Concentration from Satel-lite observations (daily average) Reprocessed L3 (ESA-CCI). Weacknowledge two anonymous referees for their time, comments, andsuggestions, which improved the final version of the manuscript.
Financial support. This research has been supported by theDeutsche Forschungsgemeinschaft (DFG, German Research Foun-dation) (grant no. 268020496 – TRR 172) and the Alfred WegenerInstitute Helmholtz Centre for Polar and Marine Research (grantno. AWI-PS-106-00).
Review statement. This paper was edited by Amy Solomon and re-viewed by two anonymous referees.
References
Aas, W., Fiebig, M., Solberg, S., and Yttri, K. E.: Monitoring oflong-range transported air pollutants in Norway, annual Report2017, NILU rapport, Norwegian Environment Agency, availableat: https://www.miljodirektoratet.no/globalassets/publikasjoner/m1395/m1395.pdf (last access: 12 March 2019), 2018.
Abbatt, J. P. D., Leaitch, W. R., Aliabadi, A. A., Bertram, A. K.,Blanchet, J.-P., Boivin-Rioux, A., Bozem, H., Burkart, J., Chang,R. Y. W., Charette, J., Chaubey, J. P., Christensen, R. J., Cirisan,A., Collins, D. B., Croft, B., Dionne, J., Evans, G. J., Fletcher,C. G., Galí, M., Ghahremaninezhad, R., Girard, E., Gong, W.,Gosselin, M., Gourdal, M., Hanna, S. J., Hayashida, H., Herber,A. B., Hesaraki, S., Hoor, P., Huang, L., Hussherr, R., Irish, V.E., Keita, S. A., Kodros, J. K., Köllner, F., Kolonjari, F., Kunkel,D., Ladino, L. A., Law, K., Levasseur, M., Libois, Q., Liggio, J.,Lizotte, M., Macdonald, K. M., Mahmood, R., Martin, R. V., Ma-son, R. H., Miller, L. A., Moravek, A., Mortenson, E., Mungall,E. L., Murphy, J. G., Namazi, M., Norman, A.-L., O’Neill, N. T.,Pierce, J. R., Russell, L. M., Schneider, J., Schulz, H., Sharma, S.,Si, M., Staebler, R. M., Steiner, N. S., Thomas, J. L., von Salzen,K., Wentzell, J. J. B., Willis, M. D., Wentworth, G. R., Xu, J.-W., and Yakobi-Hancock, J. D.: Overview paper: New insightsinto aerosol and climate in the Arctic, Atmos. Chem. Phys., 19,2527–2560, https://doi.org/10.5194/acp-19-2527-2019, 2019.
Alexeev, V. A. and Jackson, C. H.: Polar amplification: is atmo-spheric heat transport important?, Clim. Dynam., 41, 533–547,2013.
Allan, J. D., Williams, P. I., Najera, J., Whitehead, J. D., Flynn,M. J., Taylor, J. W., Liu, D., Darbyshire, E., Carpenter, L. J.,Chance, R., Andrews, S. J., Hackenberg, S. C., and McFiggans,G.: Iodine observed in new particle formation events in the Arcticatmosphere during ACCACIA, Atmos. Chem. Phys., 15, 5599–5609, https://doi.org/10.5194/acp-15-5599-2015, 2015.
Asmi, E., Frey, A., Virkkula, A., Ehn, M., Manninen, H. E., Ti-monen, H., Tolonen-Kivimäki, O., Aurela, M., Hillamo, R.,and Kulmala, M.: Hygroscopicity and chemical composition ofAntarctic sub-micrometre aerosol particles and observations ofnew particle formation, Atmos. Chem. Phys., 10, 4253–4271,https://doi.org/10.5194/acp-10-4253-2010, 2010.
S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic 14359
Asmi, E., Kondratyev, V., Brus, D., Laurila, T., Lihavainen, H.,Backman, J., Vakkari, V., Aurela, M., Hatakka, J., Viisanen, Y.,Uttal, T., Ivakhov, V., and Makshtas, A.: Aerosol size distributionseasonal characteristics measured in Tiksi, Russian Arctic, At-mos. Chem. Phys., 16, 1271–1287, https://doi.org/10.5194/acp-16-1271-2016, 2016.
Augustin-Bauditz, S., Wex, H., Denjean, C., Hartmann, S., Schnei-der, J., Schmidt, S., Ebert, M., and Stratmann, F.: Laboratory-generated mixtures of mineral dust particles with biological sub-stances: characterization of the particle mixing state and immer-sion freezing behavior, Atmos. Chem. Phys., 16, 5531–5543,https://doi.org/10.5194/acp-16-5531-2016, 2016.
Becagli, S., Lazzara, L., Marchese, C., Dayan, U., Ascanius, S. E.,Cacciani, M., Caiazzo, L., Di Biagio, C., Di Iorio, T., Di Sarra,A., and Eriksen, P.: Relationships linking primary production,sea ice melting, and biogenic aerosol in the Arctic, Atmos. Env-iron., 136, 1–15, 2016.
Bi, H., Zhang, J., Wang, Y., Zhang, Z., Zhang, Y., Fu, M., Huang,H., and Xu, X.: Arctic Sea Ice Volume Changes in Terms ofAge as Revealed From Satellite Observations, IEEE J. Sel. Top.Appl., 11, 2223–2237, 2018.
Bintanja, R., Van der Linden, E. C., and Hazeleger, W.: Boundarylayer stability and Arctic climate change: A feedback study usingEC-Earth, Clim. Dynam., 39, 2659–2673, 2012.
Burkart, J., Hodshire, A. L., Mungall, E. L., Pierce, J. R., Collins, D.B., Ladino, L. A., Lee, A. K., Irish, V., Wentzell, J. J., Liggio, J.,and Papakyriakou, T.: Organic condensation and particle growthto CCN sizes in the summertime marine Arctic is driven by ma-terials more semivolatile than at continental sites, Geophys. Res.Lett., 44, 10725–10734, https://doi.org/10.1002/2017GL075671,2017a.
Burkart, J., Willis, M. D., Bozem, H., Thomas, J. L., Law, K.,Hoor, P., Aliabadi, A. A., Köllner, F., Schneider, J., Herber,A., Abbatt, J. P. D., and Leaitch, W. R.: Summertime observa-tions of elevated levels of ultrafine particles in the high Arcticmarine boundary layer, Atmos. Chem. Phys., 17, 5515–5535,https://doi.org/10.5194/acp-17-5515-2017, 2017b.
Chang, R. Y.-W., Leck, C., Graus, M., Müller, M., Paatero, J.,Burkhart, J. F., Stohl, A., Orr, L. H., Hayden, K., Li, S.-M.,Hansel, A., Tjernström, M., Leaitch, W. R., and Abbatt, J.P. D.: Aerosol composition and sources in the central ArcticOcean during ASCOS, Atmos. Chem. Phys., 11, 10619–10636,https://doi.org/10.5194/acp-11-10619-2011, 2011.
Cohen, J., Screen, J. A., Furtado, J. C., Barlow, M., Whittle-ston, D., Coumou, D., Francis, J., Dethloff, K., Entekhabi,D., Overland, J., and Jones, J.: Recent Arctic amplificationand extreme mid-latitude weather, Nat. Geosci., 7, 627–637,https://doi.org/10.1038/ngeo2234, 2014.
Collins, D. B., Burkart, J., Chang, R. Y.-W., Lizotte, M., Boivin-Rioux, A., Blais, M., Mungall, E. L., Boyer, M., Irish, V.E., Massé, G., Kunkel, D., Tremblay, J.-É., Papakyriakou, T.,Bertram, A. K., Bozem, H., Gosselin, M., Levasseur, M., andAbbatt, J. P. D.: Frequent ultrafine particle formation and growthin Canadian Arctic marine and coastal environments, Atmos.Chem. Phys., 17, 13119–13138, https://doi.org/10.5194/acp-17-13119-2017, 2017.
Conover, R. J. and Huntley, M.: Copepods in ice-covered seas –distribution, adaptations to seasonally limited food, metabolism,
growth patterns and life cycle strategies in polar seas, J. MarineSyst., 2, 1–41, 1991.
Croft, B., Wentworth, G. R., Martin, R. V., Leaitch, W. R., Mur-phy, J. G., Murphy, B. N., Kodros, J. K., Abbatt, J. P., and Pierce,J. R.: Contribution of Arctic seabird-colony ammonia to atmo-spheric particles and cloud-albedo radiative effect, Nat. Com-mun., 7, 13444, https://doi.org/10.1038/ncomms13444, 2016.
Dall’Osto, M., Beddows, D. C. S., Tunved, P., Krejci, R., Ström,J., Hansson, H. C., Yoon, Y. J., Park, K. T., Becagli, S.,Udisti, R., and Onasch, T.: Arctic sea ice melt leads to at-mospheric new particle 70 formation, Sci. Rep., 7, 3318,https://doi.org/10.1038/s41598-017-03328-1, 2017.
Dall’Osto, M., Geels, C., Beddows, D. C. S., Boertmann, D., Lange,R., Nøjgaard, J. K., Harrison, R. M., Simo, R., Skov, H., andMassling, A.: Regions of open water and melting sea ice drivenew particle formation in North East Greenland, Sci. Rep., 8,6109, https://doi.org/10.1038/s41598-018-24426-8, 2018a.
Dall’Osto, M., Beddows, D. C. S., Asmi, A., Poulain, L., Hao, L.,Freney, E., Allan, J. D., Canagaratna, M., Crippa, M., Bianchi, F.,and De Leeuw, G.: Novel insights on new particle formation de-rived from a pan-european observing system, Sci. Rep., 8, 1482,https://doi.org/10.1038/s41598-017-17343-9, 2018b.
Dall’Osto, M., Beddows, D. C. S., Tunved, P., Harrison, R. M.,Lupi, A., Vitale, V., Becagli, S., Traversi, R., Park, K.-T., Yoon,Y. J., Massling, A., Skov, H., Lange, R., Strom, J., and Krejci,R.: Simultaneous measurements of aerosol size distributions atthree sites in the European high Arctic, Atmos. Chem. Phys., 19,7377–7395, https://doi.org/10.5194/acp-19-7377-2019, 2019.
Draxler, R. R. and Rolph, G. D.: HYSPLIT (HYbrid Single-ParticleLagrangian Integrated Trajectory), NOAA Air Resources Labo-ratory, Silver Spring, USA, 2012.
Dunne, E. M., Gordon, H., Kürten, A., Almeida, J., Duplissy, J.,Williamson, C., Ortega, I. K., Pringle, K. J., Adamov, A., Bal-tensperger, U., and Barmet, P.: Global atmospheric particle for-mation from CERN CLOUD measurements, Science, 354, 1119–1124, 2016.
Egerer, U., Gottschalk, M., Siebert, H., Ehrlich, A., and Wendisch,M.: The new BELUGA setup for collocated turbulence and ra-diation measurements using a tethered balloon: first applicationsin the cloudy Arctic boundary layer, Atmos. Meas. Tech., 12,4019–4038, https://doi.org/10.5194/amt-12-4019-2019, 2019.
Ehn, M., Petäjä, T., Aufmhoff, H., Aalto, P., Hämeri, K., Arnold,F., Laaksonen, A., and Kulmala, M.: Hygroscopic properties ofultrafine aerosol particles in the boreal forest: diurnal variation,solubility and the influence of sulfuric acid, Atmos. Chem. Phys.,7, 211–222, https://doi.org/10.5194/acp-7-211-2007, 2007.
Fetterer, F., Knowles, K., Meier, W., and Savoie, M.: Sea ice index.National Snow and Ice Data Center, Boulder, CO, digital me-dia, available at: http://nsidc.org/data/g02135.html (last access:25 May 2019), 2002.
Fomba, K. W., Müller, K., van Pinxteren, D., Poulain, L., vanPinxteren, M., and Herrmann, H.: Long-term chemical charac-terization of tropical and marine aerosols at the Cape VerdeAtmospheric Observatory (CVAO) from 2007 to 2011, Atmos.Chem. Phys., 14, 8883–8904, https://doi.org/10.5194/acp-14-8883-2014, 2014.
Freud, E., Krejci, R., Tunved, P., Leaitch, R., Nguyen, Q. T.,Massling, A., Skov, H., and Barrie, L.: Pan-Arctic aerosol num-ber size distributions: seasonality and transport patterns, At-
Galloway, J. N., Savoie, D. L., Keene, W. C., and Prospero, J. M.:The temporal and spatial variability of scavenging ratios for NSSsulfate, nitrate, methanesulfonate and sodium in the atmosphereover the North Atalantic Ocean, Atmos. Environ. A-Gen., 27,235–250, 1993.
Giamarelou, M., Eleftheriadis, K., Nyeki, S., Tunved, P., Torseth,K., and Biskos, G.: Indirect evidence of the composition of nu-cleation mode atmospheric particles in the high Arctic, J. Geo-phys. Res.-Atmos., 121, 965–975, 2016.
Graversen, R. G. and Wang, M.: Polar amplification in a coupledclimate model with locked albedo, Clim. Dynam., 33, 629–643,2009.
Gysel, M. and Stratmann, F.: WP3 – NA3: In-situ chemical, phys-ical and optical properties of aerosols, Deliverable D3.11: Stan-dardized protocol for CCN measurements, Tech. rep., availableat: http://www.actris.net (last access: 25 May 2019), 2013.
Gysel, M., McFiggans, G. B., and Coe, H.: Inversion of tandemdifferential mobility analyser (TDMA) measurements, J. AerosolSci., 40, 134–151, 2009.
Heintzenberg, J., Tunved, P., Galí, M., and Leck, C.: New par-ticle formation in the Svalbard region 2006–2015, Atmos.Chem. Phys., 17, 6153–6175, https://doi.org/10.5194/acp-17-6153-2017, 2017.
Herenz, P., Wex, H., Mangold, A., Laffineur, Q., Gorodetskaya, I.V., Fleming, Z. L., Panagi, M., and Stratmann, F.: CCN measure-ments at the Princess Elisabeth Antarctica research station dur-ing three austral summers, Atmos. Chem. Phys., 19, 275–294,https://doi.org/10.5194/acp-19-275-2019, 2019.
Hirsikko, A., Bergman, T., Laakso, L., Dal Maso, M., Riipinen,I., Hõrrak, U., and Kulmala, M.: Identification and classificationof the formation of intermediate ions measured in boreal forest,Atmos. Chem. Phys., 7, 201–210, https://doi.org/10.5194/acp-7-201-2007, 2007.
Huang, S., Wu, Z., Poulain, L., van Pinxteren, M., Merkel, M.,Assmann, D., Herrmann, H., and Wiedensohler, A.: Source ap-portionment of the organic aerosol over the Atlantic Oceanfrom 53◦ N to 53◦ S: significant contributions from marine emis-sions and long-range transport, Atmos. Chem. Phys., 18, 18043–18062, https://doi.org/10.5194/acp-18-18043-2018, 2018.
Jayaratne, E. R., Pushpawela, B., and Morawska, L.: Temporal evo-lution of charged and neutral nanoparticle concentrations dur-ing atmospheric new particle formation events and its implica-tions for ion-induced nucleation, Front. Env. Sci. Eng., 10, 13,https://doi.org/10.1007/s11783-016-0862-x, 2016.
Jeffries, M. O. and Richter-Menge, J.: State of the climate in 2011:The Arctic, B. Am. Meteorol. Soc., 93, 127–148, 2012.
Jokinen, T., Sipilä, M., Kontkanen, J., Vakkari, V., Tisler, P., Du-plissy, E. M., Junninen, H., Kangasluoma, J., Manninen, H. E.,Petäjä, T., and Kulmala, M.: Ion-induced sulfuric acid–ammonianucleation drives particle formation in coastal Antarctica, Sci.Adv., 4, 9744, https://doi.org/10.1126/sciadv.aat9744, 2018.
Karl, M., Leck, C., Gross, A., and Pirjola, L.: A study of new parti-cle formation in the marine boundary layer over the central ArcticOcean using a flexible multicomponent aerosol dynamic model,Tellus B, 64, 17158, https://doi.org/10.3402/tellusb.v64i0.17158,2012.
Karl, M., Leck, C., Coz, E., and Heintzenberg, J.: Marine nanogelsas a source of atmospheric nanoparticles in the high Arctic, Geo-phys. Res. Lett., 40, 3738–3743, 2013.
Keene, W. C., Maring, H., Maben, J. R., Kieber, D. J., Pszenny, A.A. P., Dahl, E. E., Izaguirre, M. A., Davis, A. J., Long, M. S.,Zhou, X., Smoydzin, L., and Sander, R.: Chemical and PhysicalCharacteristics of Nascent Aerosols Produced by Bursting Bub-bles at a Model Air-Sea Interface, J. Geophys. Res.-Atmos., 112,D21202, https://doi.org/10.1029/2007JD008464, 2007.
Kerminen, V. M., Aurela, M., Hillamo, R. E., and Virkkula, A.:Formation of particulate MSA: deductions from size distribu-tion measurements in the Finnish Arctic, Tellus B, 49, 159–171,1997.
Kerminen, V.-M., Paramonov, M., Anttila, T., Riipinen, I., Foun-toukis, C., Korhonen, H., Asmi, E., Laakso, L., Lihavainen, H.,Swietlicki, E., Svenningsson, B., Asmi, A., Pandis, S. N., Kul-mala, M., and Petäjä, T.: Cloud condensation nuclei productionassociated with atmospheric nucleation: a synthesis based on ex-isting literature and new results, Atmos. Chem. Phys., 12, 12037–12059, https://doi.org/10.5194/acp-12-12037-2012, 2012.
Kerminen, V. M., Chen, X., Vakkari, V., Petäjä, T., Kulmala, M.,and Bianchi, F.: Atmospheric new particle formation and growth:review of field observations, Environ. Res. Lett., 13, 103003,https://doi.org/10.1088/1748-9326/aadf3c, 2018.
Kim, J., Ahlm, L., Yli-Juuti, T., Lawler, M., Keskinen, H., Tröstl,J., Schobesberger, S., Duplissy, J., Amorim, A., Bianchi, F., Don-ahue, N. M., Flagan, R. C., Hakala, J., Heinritzi, M., Jokinen, T.,Kürten, A., Laaksonen, A., Lehtipalo, K., Miettinen, P., Petäjä,T., Rissanen, M. P., Rondo, L., Sengupta, K., Simon, M., Tomé,A., Williamson, C., Wimmer, D., Winkler, P. M., Ehrhart, S., Ye,P., Kirkby, J., Curtius, J., Baltensperger, U., Kulmala, M., Lehti-nen, K. E. J., Smith, J. N., Riipinen, I., and Virtanen, A.: Hy-groscopicity of nanoparticles produced from homogeneous nu-cleation in the CLOUD experiments, Atmos. Chem. Phys., 16,293–304, https://doi.org/10.5194/acp-16-293-2016, 2016.
Knudsen, E. M., Heinold, B., Dahlke, S., Bozem, H., Crewell, S.,Gorodetskaya, I. V., Heygster, G., Kunkel, D., Maturilli, M.,Mech, M., Viceto, C., Rinke, A., Schmithüsen, H., Ehrlich, A.,Macke, A., Lüpkes, C., and Wendisch, M.: Meteorological con-ditions during the ACLOUD/PASCAL field campaign near Sval-bard in early summer 2017, Atmos. Chem. Phys., 18, 17995–18022, https://doi.org/10.5194/acp-18-17995-2018, 2018.
Köhler, H.: The nucleus in and the growth of hygroscopic droplets,T. Faraday Soc., 32, 1152–1161, 1936.
Köllner, F., Schneider, J., Willis, M. D., Klimach, T., Helleis, F.,Bozem, H., Kunkel, D., Hoor, P., Burkart, J., Leaitch, W. R.,Aliabadi, A. A., Abbatt, J. P. D., Herber, A. B., and Borrmann,S.: Particulate trimethylamine in the summertime Canadian highArctic lower troposphere, Atmos. Chem. Phys., 17, 13747–13766, https://doi.org/10.5194/acp-17-13747-2017, 2017.
Kulmala, M., Maso, M. D., Mäkelä, J. M., Pirjola, L., Väkevä, M.,Aalto, P., Miikkulainen, P., Hämeri, K., and O’dowd, C. D.: Onthe formation, growth and composition of nucleation mode par-ticles, Tellus B, 53, 479–490, 2001.
Kulmala, M., Petäjä, T., Nieminen, T., Sipilä, M., Manninen,H. E., Lehtipalo, K., Dal Maso, M., Aalto, P. P., Junninen,H., Paasonen, P., and Riipinen, I.: Measurement of the nucle-ation of atmospheric aerosol particles, Nat. Protoc., 7, 1651,https://doi.org/10.1038/nprot.2012.091, 2012.
S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic 14361
Kurtén, T., Torpo, L., Sundberg, M. R., Kerminen, V.-M.,Vehkamäki, H., and Kulmala, M.: Estimating the NH3 : H2SO4ratio of nucleating clusters in atmospheric conditions using quan-tum chemical methods, Atmos. Chem. Phys., 7, 2765–2773,https://doi.org/10.5194/acp-7-2765-2007, 2007.
Kyrö, E.-M., Kerminen, V.-M., Virkkula, A., Dal Maso, M., Parsh-intsev, J., Ruíz-Jimenez, J., Forsström, L., Manninen, H. E.,Riekkola, M.-L., Heinonen, P., and Kulmala, M.: Antarctic newparticle formation from continental biogenic precursors, At-mos. Chem. Phys., 13, 3527–3546, https://doi.org/10.5194/acp-13-3527-2013, 2013.
Leaitch, W. R., Strapp, J. W., Isaac, G. A., and Hudson, J. G.: Clouddroplet nucleation and cloud scavenging of aerosol sulphate inpolluted atmospheres, Tellus B, 38, 328–344, 1986.
Leaitch, W. R., Sharma, S., Huang, L., Toom-Sauntry, D.,Chivulescu, A., Macdonald, A. M., von Salzen, K., Pierce, J. R.,Bertram, A. K., Schroder, J. C., Shantz, N. C., Chang, R. Y.-W.,and Norman, A.-L.: Dimethyl sulfide control of the clean sum-mertime Arctic aerosol and cloud, Elem. Sci. Anth., 1, 00017,https://doi.org/10.12952/journal.elementa.000017, 2013.
Leaitch, W. R., Korolev, A., Aliabadi, A. A., Burkart, J., Willis,M. D., Abbatt, J. P. D., Bozem, H., Hoor, P., Köllner, F.,Schneider, J., Herber, A., Konrad, C., and Brauner, R.: Ef-fects of 20–100 nm particles on liquid clouds in the cleansummertime Arctic, Atmos. Chem. Phys., 16, 11107–11124,https://doi.org/10.5194/acp-16-11107-2016, 2016.
Leck, C., Norman, M., Bigg, E. K., and Hillamo, R.: Chemi-cal composition and sources of the high Arctic aerosol rele-vant for cloud formation, J. Geophys. Res.-Atmos., 107, 4135,https://doi.org/10.1029/2001JD001463, 2002.
Lehtinen, K. E., Dal Maso, M., Kulmala, M., and Kerminen, V.M.: Estimating nucleation rates from apparent particle forma-tion rates and vice versa: Revised formulation of the Kerminen–Kulmala equation, J. Aerosol Sci., 38, 988–994, 2007.
Levasseur, M.: Impact of Arctic meltdown on the mi-crobial cycling of sulphur, Nat. Geosci., 6, 691–700,https://doi.org/10.1038/ngeo1910, 2013.
Macke, A. and Flores, H.: The Expeditions PS106/1 and 2of the Research Vessel POLARSTERN to the Arctic Oceanin 2017. Berichte zur Polar- und Meeresforschung, Reportson polar and marine research, Bremerhaven, Alfred We-gener Institute for Polar and Marine Research, 719, 171,https://doi.org/10.2312/BzPM_0719_2018, 2018.
Manninen, H. E., Nieminen, T., Asmi, E., Gagné, S., Häkkinen,S., Lehtipalo, K., Aalto, P., Vana, M., Mirme, A., Mirme, S.,Hõrrak, U., Plass-Dülmer, C., Stange, G., Kiss, G., Hoffer, A.,Töro, N., Moerman, M., Henzing, B., de Leeuw, G., Brinken-berg, M., Kouvarakis, G. N., Bougiatioti, A., Mihalopoulos, N.,O’Dowd, C., Ceburnis, D., Arneth, A., Svenningsson, B., Swi-etlicki, E., Tarozzi, L., Decesari, S., Facchini, M. C., Birmili, W.,Sonntag, A., Wiedensohler, A., Boulon, J., Sellegri, K., Laj, P.,Gysel, M., Bukowiecki, N., Weingartner, E., Wehrle, G., Laakso-nen, A., Hamed, A., Joutsensaari, J., Petäjä, T., Kerminen, V.-M.,and Kulmala, M.: EUCAARI ion spectrometer measurements at12 European sites – analysis of new particle formation events, At-mos. Chem. Phys., 10, 7907–7927, https://doi.org/10.5194/acp-10-7907-2010, 2010.
Manninen, H. E., Franchin, A., Schobesberger, S., Hirsikko, A.,Hakala, J., Skromulis, A., Kangasluoma, J., Ehn, M., Junninen,
H., Mirme, A., Mirme, S., Sipilä, M., Petäjä, T., Worsnop, D. R.,and Kulmala, M.: Characterisation of corona-generated ions usedin a Neutral cluster and Air Ion Spectrometer (NAIS), Atmos.Meas. Tech., 4, 2767–2776, https://doi.org/10.5194/amt-4-2767-2011, 2011.
Maslanik, J. and Stroeve, J.: Near-Real-Time DMSP SSMIS DailyPolar Gridded Sea Ice Concentrations, 1 Boulder, ColoradoUSA. NASA National Snow and Ice Data Center Distributed Ac-tive Archive Center, https://doi.org/10.5067/U8C09DWVX9LM,1999.
Massling, A., Niedermeier, N., Hennig, T., Fors, E. O., Swietlicki,E., Ehn, M., Hämeri, K., Villani, P., Laj, P., Good, N., McFig-gans, G., and Wiedensohler, A.: Results and recommendationsfrom an intercomparison of six Hygroscopicity-TDMA systems,Atmos. Meas. Tech., 4, 485–497, https://doi.org/10.5194/amt-4-485-2011, 2011.
Mauritsen, T., Sedlar, J., Tjernström, M., Leck, C., Martin,M., Shupe, M., Sjogren, S., Sierau, B., Persson, P. O. G.,Brooks, I. M., and Swietlicki, E.: An Arctic CCN-limitedcloud-aerosol regime, Atmos. Chem. Phys., 11, 165–173,https://doi.org/10.5194/acp-11-165-2011, 2011.
Meier, W. N., Hovelsrud, G. K., van Oort, B. E., Key, J. R., Kovacs,K. M., Michel, C., Haas, C., Granskog, M. A., Gerland, S., Per-ovich, D. K., and Makshtas, A.: Arctic sea ice in transformation:A review of recent observed changes and impacts on biology andhuman activity, Rev. Geophys., 52, 185–217, 2014.
Merikanto, J., Spracklen, D. V., Mann, G. W., Pickering, S. J., andCarslaw, K. S.: Impact of nucleation on global CCN, Atmos.Chem. Phys., 9, 8601–8616, https://doi.org/10.5194/acp-9-8601-2009, 2009.
Mirme, A., Tamm, E., Mordas, G., Vana, M., Uin, J., Mirme, S.,Bernotas, T., Laakso, L., Hirsikko, A., and Kulmala, M.: Awide-range multi-channel Air Ion Spectrometer, Boreal Environ.Res.,12, 247–264, 2007.
Mirme, S. and Mirme, A.: The mathematical principles and designof the NAIS – a spectrometer for the measurement of cluster ionand nanometer aerosol size distributions, Atmos. Meas. Tech., 6,1061–1071, https://doi.org/10.5194/amt-6-1061-2013, 2013.
Miyazaki, Y., Kawamura, K., and Sawano, M.: Size distri-butions of organic nitrogen and carbon in remote ma-rine aerosols: Evidence of marine biological origin basedon their isotopic ratios, Geophys. Res. Lett., 37, L06803,https://doi.org/10.1029/2010GL042483, 2010.
Müller, K., Lehmann, S., van Pinxteren, D., Gnauk, T., Nieder-meier, N., Wiedensohler, A., and Herrmann, H.: Particle charac-terization at the Cape Verde atmospheric observatory during the2007 RHaMBLe intensive, Atmos. Chem. Phys., 10, 2709–2721,https://doi.org/10.5194/acp-10-2709-2010, 2010.
Napari, I., Noppel, M., Vehkamäki, H., and Kulmala, M.:Parametrization of ternary nucleation rates for H2SO4-NH3-H2O vapors, J. Geophys. Res.-Atmos., 107, AAC 6-1–AAC 6-6,https://doi.org/10.1029/2002JD002132, 2002.
Nguyen, Q. T., Glasius, M., Sørensen, L. L., Jensen, B., Skov,H., Birmili, W., Wiedensohler, A., Kristensson, A., Nøjgaard,J. K., and Massling, A.: Seasonal variation of atmospheric par-ticle number concentrations, new particle formation and atmo-spheric oxidation capacity at the high Arctic site Villum ResearchStation, Station Nord, Atmos. Chem. Phys., 16, 11319–11336,https://doi.org/10.5194/acp-16-11319-2016, 2016.
14362 S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic
Nicolaus, M.: Shipborne visual observations of Arctic seaice during POLARSTERN cruise PS106, PANGAEA,https://doi.org/10.1594/PANGAEA.889264, 2018.
Nieminen, T., Kerminen, V.-M., Petäjä, T., Aalto, P. P., Arshinov,M., Asmi, E., Baltensperger, U., Beddows, D. C. S., Beukes, J.P., Collins, D., Ding, A., Harrison, R. M., Henzing, B., Hooda,R., Hu, M., Hõrrak, U., Kivekäs, N., Komsaare, K., Krejci, R.,Kristensson, A., Laakso, L., Laaksonen, A., Leaitch, W. R., Li-havainen, H., Mihalopoulos, N., Németh, Z., Nie, W., O’Dowd,C., Salma, I., Sellegri, K., Svenningsson, B., Swietlicki, E.,Tunved, P., Ulevicius, V., Vakkari, V., Vana, M., Wiedensohler,A., Wu, Z., Virtanen, A., and Kulmala, M.: Global analysis ofcontinental boundary layer new particle formation based on long-term measurements, Atmos. Chem. Phys., 18, 14737–14756,https://doi.org/10.5194/acp-18-14737-2018, 2018.
Orellana, M. V., Matrai, P. A., Leck, C., Rauschenberg, C. D., Lee,A. M., and Coz, E.: Marine microgels as a source of cloud con-densation nuclei in the high Arctic, P. Natl. Acad. Sci. USA, 108,13612–13617, 2011.
Overland, J. E., Wood, K. R., and Wang, M.: Warm Arctic – coldcontinents: climate impacts of the newly open Arctic Sea, Po-lar Res., 30, 15787, https://doi.org/10.3402/polar.v30i0.15787,2011.
Park, K., Kim, G., Kim, J. S., Yoon, Y. J., Cho, H. J., and Ström,J.: Mixing state of size-selected submicrometer particles in theArctic in May and September 2012, Environ. Sci. Technol., 48,909–919, 2014.
Park, K.-T., Jang, S., Lee, K., Yoon, Y. J., Kim, M.-S., Park, K., Cho,H.-J., Kang, J.-H., Udisti, R., Lee, B.-Y., and Shin, K.-H.: Ob-servational evidence for the formation of DMS-derived aerosolsduring Arctic phytoplankton blooms, Atmos. Chem. Phys., 17,9665–9675, https://doi.org/10.5194/acp-17-9665-2017, 2017.
Petters, M. D. and Kreidenweis, S. M.: A single parameterrepresentation of hygroscopic growth and cloud condensa-tion nucleus activity, Atmos. Chem. Phys., 7, 1961–1971,https://doi.org/10.5194/acp-7-1961-2007, 2007.
Pfeifer, S., Birmili, W., Schladitz, A., Müller, T., Nowak, A.,and Wiedensohler, A.: A fast and easy-to-implement inver-sion algorithm for mobility particle size spectrometers con-sidering particle number size distribution information out-side of the detection range, Atmos. Meas. Tech., 7, 95–105,https://doi.org/10.5194/amt-7-95-2014, 2014.
Pichelstorfer, L., Stolzenburg, D., Ortega, J., Karl, T., Kokkola,H., Laakso, A., Lehtinen, K. E. J., Smith, J. N., McMurry, P.H., and Winkler, P. M.: Resolving nanoparticle growth mecha-nisms from size- and time-dependent growth rate analysis, At-mos. Chem. Phys., 18, 1307–1323, https://doi.org/10.5194/acp-18-1307-2018, 2018.
Pithan, F. and Mauritsen, T.: Arctic amplification dominated bytemperature feedbacks in contemporary climate models, Nat.Geosci., 7, 181–184, https://doi.org/10.1038/ngeo2071, 2014.
Polashenski, C., Golden, K. M., Perovich, D. K., Skyllingstad, E.,Arnsten, A., Stwertka, C., and Wright, N.: Percolation blockage:A process that enables melt pond formation on first year Arcticsea ice, J. Geophys. Res.-Oceans, 122, 413–440, 2017.
Praetorius, S., Rugenstein, M., Persad, G., and Caldeira,K.: Global and Arctic climate sensitivity enhanced bychanges in North Pacific heat flux, Nat. Commun., 9, 3124,https://doi.org/10.1038/s41467-018-05337-8, 2018.
Quinn, P. K., Collins, D. B., Grassian, V. H., Prather, K. A., andBates, T. S.: Chemistry and Related Properties of Freshly Emit-ted Sea Spray Aerosol, Chem. Rev., 115, 4383–4399, 2015.
Rampal, P., Weiss, J., and Marsan, D.: Positive trend inthe mean speed and deformation rate of Arctic seaice, 1979–2007, J. Geophys. Res.-Oceans, 114, C05013,https://doi.org/10.1029/2008JC005066, 2009.
Riccobono, F., Schobesberger, S., Scott, C. E., Dommen, J., Ortega,I. K., Rondo, L., Almeida, J., Amorim, A., Bianchi, F., Breiten-lechner, M., and David, A.: Oxidation products of biogenic emis-sions contribute to nucleation of atmospheric particles, Science,344, 717–721, 2014.
Roberts, G. C. and Nenes, A.: A continuous-flow streamwisethermal-gradient CCN chamber for atmospheric measurements,Aerosol Sci. Tech., 39, 206–221, 2005.
Rothenberg, D. and Wang, C.: Metamodeling of droplet activationfor global climate models, J. Atmos. Sci., 73, 1255–1272, 2016.
Schobesberger, S., Junninen, H., Bianchi, F., Lönn, G., Ehn, M.,Lehtipalo, K., Dommen, J., Ehrhart, S., Ortega, I. K., Franchin,A., and Nieminen, T.: Molecular understanding of atmosphericparticle formation from sulfuric acid and large oxidized organicmolecules, P. Natl. Acad. Sci. USA, 110, 17223–17228, 2013.
Schobesberger, S., Franchin, A., Bianchi, F., Rondo, L., Duplissy, J.,Kürten, A., Ortega, I. K., Metzger, A., Schnitzhofer, R., Almeida,J., Amorim, A., Dommen, J., Dunne, E. M., Ehn, M., Gagné, S.,Ickes, L., Junninen, H., Hansel, A., Kerminen, V.-M., Kirkby,J., Kupc, A., Laaksonen, A., Lehtipalo, K., Mathot, S., Onnela,A., Petäjä, T., Riccobono, F., Santos, F. D., Sipilä, M., Tomé,A., Tsagkogeorgas, G., Viisanen, Y., Wagner, P. E., Wimmer, D.,Curtius, J., Donahue, N. M., Baltensperger, U., Kulmala, M., andWorsnop, D. R.: On the composition of ammonia–sulfuric-acidion clusters during aerosol particle formation, Atmos. Chem.Phys., 15, 55–78, https://doi.org/10.5194/acp-15-55-2015, 2015.
Screen, J. A. and Simmonds, I.: The central role of diminishing seaice in recent Arctic temperature amplification, Nature, 464, 1334,https://doi.org/10.1038/nature09051, 2010.
Serreze, M. C. and Barry, R. G.: Processes and impacts of Arcticamplification: A research synthesis, Global Planet. Change, 77,85–96, 2011.
Sipilä, M., Sarnela, N., Jokinen, T., Henschel, H., Junninen, H.,Kontkanen, J., Richters, S., Kangasluoma, J., Franchin, A.,Peräkylä, O., and Rissanen, M. P.: Molecular-scale evidence ofaerosol particle formation via sequential addition of HIO3, Na-ture, 537, 532–534, https://doi.org/10.1038/nature19314, 2016.
Smith, J. N., Barsanti, K. C., Friedli, H. R., Ehn, M., Kulmala, M.,Collins, D. R., Scheckman, J. H., Williams, B. J., and McMurry,P. H.: Observations of aminium salts in atmospheric nanoparti-cles and possible climatic implications, P. Natl. Acad. Sci. USA,107, 6634–6639, 2010.
Spielhagen, R. F., Werner, K., Sørensen, S. A., Zamelczyk, K., Kan-diano, E., Budeus, G., Husum, K., Marchitto, T. M., and Hald,M.: Enhanced modern heat transfer to the Arctic by warm At-lantic water, Science, 331, 450–453, 2011.
Stefels, J., Steinke, M., Turner, S., Malin, G., and Belviso, S.: Envi-ronmental constraints on the production and removal of the cli-matically active gas dimethylsulphide (DMS) and implicationsfor ecosystem modelling, Biogeochemistry, 83, 245–275, 2007.
Ström, J., Engvall, A. C., Delbart, F., Krejci, R., and Treffeisen, R.:On small particles in the Arctic summer boundary layer: observa-
S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic 14363
tions at two different heights near Ny-Ålesund, Svalbard, TellusB, 61, 473–482, 2009.
Taylor, P. C., Cai, M., Hu, A., Meehl, J., Washington, W., andZhang, G. J.: A decomposition of feedback contributions to polarwarming amplification, J. Climate, 26, 7023–7043, 2013.
Tremblay, S., Picard, J.-C., Bachelder, J. O., Lutsch, E., Strong,K., Fogal, P., Leaitch, W. R., Sharma, S., Kolonjari, F., Cox,C. J., Chang, R. Y.-W., and Hayes, P. L.: Characterization ofaerosol growth events over Ellesmere Island during the sum-mers of 2015 and 2016, Atmos. Chem. Phys., 19, 5589–5604,https://doi.org/10.5194/acp-19-5589-2019, 2019.
Tritscher, T., Dommen, J., DeCarlo, P. F., Gysel, M., Barmet,P. B., Praplan, A. P., Weingartner, E., Prévôt, A. S. H., Ri-ipinen, I., Donahue, N. M., and Baltensperger, U.: Volatil-ity and hygroscopicity of aging secondary organic aerosolin a smog chamber, Atmos. Chem. Phys., 11, 11477–11496,https://doi.org/10.5194/acp-11-11477-2011, 2011.
Turpin, B. J. and Lim, H. J.: Species contributions to PM2.5 massconcentrations: Revisiting common assumptions for estimatingorganic mass, Aerosol Sci. Tech., 35, 602–610, 2001.
Vakkari, V., Tiitta, P., Jaars, K., Croteau, P., Beukes, J. P., Josipovic,M., Kerminen, V. M., Kulmala, M., Venter, A. D., van Zyl, P.G., and Worsnop, D. R.: Reevaluating the contribution of sul-furic acid and the origin of organic compounds in atmosphericnanoparticle growth, Geophys. Res. Lett., 42, 10–486, 2015.
Van Pinxteren, M., Barthel, S., Fomba, K. W., Müller, K., VonTümpling, W., and Herrmann, H.: The Influence of Environ-mental Drivers on the Enrichment of Organic Carbon in the SeaSurface Microlayer and in Submicron Aerosol Particles – Mea-surements from the Atlantic Ocean, Elem. Sci. Anth., 5, 35,https://doi.org/10.1525/elementa.225, 2017.
Vavrus, S.: The impact of cloud feedbacks on Arctic climate undergreenhouse forcing, J. Climate, 17, 603–615, 2004.
Wagner, R., Manninen, H. E., Franchin, A., Lehtipalo, K., Mirme,S., Steiner, G., Petäjä, T., and Kulmala, M.: On the accuracy ofion measurements using a Neutral cluster and Air Ion Spectrom-eter, Boreal Environ. Res., 21, 230–241, 2016.
Wagner, R., Yan, C., Lehtipalo, K., Duplissy, J., Nieminen, T., Kan-gasluoma, J., Ahonen, L. R., Dada, L., Kontkanen, J., Manni-nen, H. E., Dias, A., Amorim, A., Bauer, P. S., Bergen, A., Bern-hammer, A.-K., Bianchi, F., Brilke, S., Mazon, S. B., Chen, X.,Draper, D. C., Fischer, L., Frege, C., Fuchs, C., Garmash, O.,Gordon, H., Hakala, J., Heikkinen, L., Heinritzi, M., Hofbauer,V., Hoyle, C. R., Kirkby, J., Kürten, A., Kvashnin, A. N., Lau-rila, T., Lawler, M. J., Mai, H., Makhmutov, V., Mauldin III, R.L., Molteni, U., Nichman, L., Nie, W., Ojdanic, A., Onnela, A.,Piel, F., Quéléver, L. L. J., Rissanen, M. P., Sarnela, N., Schall-hart, S., Sengupta, K., Simon, M., Stolzenburg, D., Stozhkov, Y.,Tröstl, J., Viisanen, Y., Vogel, A. L., Wagner, A. C., Xiao, M.,Ye, P., Baltensperger, U., Curtius, J., Donahue, N. M., Flagan, R.C., Gallagher, M., Hansel, A., Smith, J. N., Tomé, A., Winkler, P.M., Worsnop, D., Ehn, M., Sipilä, M., Kerminen, V.-M., Petäjä,T., and Kulmala, M.: The role of ions in new particle formationin the CLOUD chamber, Atmos. Chem. Phys., 17, 15181–15197,https://doi.org/10.5194/acp-17-15181-2017, 2017.
Walsh, J. E.: Intensified warming of the Arctic: Causes and impactson middle latitudes, Global Planet. Change, 117, 52–63, 2014.
Weller, R., Schmidt, K., Teinilä, K., and Hillamo, R.: Natural newparticle formation at the coastal Antarctic site Neumayer, Atmos.
Wendisch, M., Macke, A., Ehrlich, A., Lüpkes, C., Mech, M.,Chechin, D., Dethloff, K., Barientos, C., Bozem, H., Brück-ner, M., and Clemen, H. C.: The Arctic Cloud Puzzle: Us-ing ACLOUD/PASCAL Multi-Platform Observations to Un-ravel the Role of Clouds and Aerosol Particles in Arc-tic Amplification, B. Am. Meteorol. Soc., 100, 841–871,https://doi.org/10.1175/BAMS-D-18-0072.1, 2019.
Wentworth, G. R., Murphy, J. G., Croft, B., Martin, R. V.,Pierce, J. R., Côté, J.-S., Courchesne, I., Tremblay, J.-É.,Gagnon, J., Thomas, J. L., Sharma, S., Toom-Sauntry, D.,Chivulescu, A., Levasseur, M., and Abbatt, J. P. D.: Ammo-nia in the summertime Arctic marine boundary layer: sources,sinks, and implications, Atmos. Chem. Phys., 16, 1937–1953,https://doi.org/10.5194/acp-16-1937-2016, 2016.
Wiedensohler, A.: An approximation of the bipolar charge distribu-tion for particles in the submicron size range, J. Aerosol Sci., 19,387–389, 1988.
Wiedensohler, A., Covert, D. S., Swietlicki, E., Aalto, P., Heintzen-berg, J., and Leck, C.: Occurrence of an ultrafine particle modeless than 20 nm in diameter in the marine boundary layer duringArctic summer and autumn, Tellus B, 48, 213–222, 1996.
Wiedensohler, A., Orsini, D., Covert, D. S., Coffmann, D., Cantrell,W., Havlicek, M., Brechtel, F. J., Russell, L. M., Weber, R. J.,Gras, J., and Hudson, J. G.: Intercomparison study of the size-dependent counting efficiency of 26 condensation particle coun-ters, Aerosol Sci. Tech., 27, 224–242, 1997.
Wiedensohler, A., Birmili, W., Nowak, A., Sonntag, A., Weinhold,K., Merkel, M., Wehner, B., Tuch, T., Pfeifer, S., Fiebig, M.,Fjäraa, A. M., Asmi, E., Sellegri, K., Depuy, R., Venzac, H., Vil-lani, P., Laj, P., Aalto, P., Ogren, J. A., Swietlicki, E., Williams,P., Roldin, P., Quincey, P., Hüglin, C., Fierz-Schmidhauser, R.,Gysel, M., Weingartner, E., Riccobono, F., Santos, S., Grün-ing, C., Faloon, K., Beddows, D., Harrison, R., Monahan, C.,Jennings, S. G., O’Dowd, C. D., Marinoni, A., Horn, H.-G.,Keck, L., Jiang, J., Scheckman, J., McMurry, P. H., Deng, Z.,Zhao, C. S., Moerman, M., Henzing, B., de Leeuw, G., Löschau,G., and Bastian, S.: Mobility particle size spectrometers: har-monization of technical standards and data structure to facili-tate high quality long-term observations of atmospheric parti-cle number size distributions, Atmos. Meas. Tech., 5, 657–685,https://doi.org/10.5194/amt-5-657-2012, 2012.
Wiedensohler, A., Wiesner, A., Weinhold, K., Birmili, W., Her-mann, M., Merkel, M., Müller, T., Pfeifer, S., Schmidt, A., Tuch,T., and Velarde, F.: Mobility particle size spectrometers: Cali-bration procedures and measurement uncertainties, Aerosol Sci.Tech., 52, 146–164, 2018.
Willis, M. D., Burkart, J., Thomas, J. L., Köllner, F., Schneider,J., Bozem, H., Hoor, P. M., Aliabadi, A. A., Schulz, H., Herber,A. B., Leaitch, W. R., and Abbatt, J. P. D.: Growth of nucle-ation mode particles in the summertime Arctic: a case study, At-mos. Chem. Phys., 16, 7663–7679, https://doi.org/10.5194/acp-16-7663-2016, 2016.
Willis, M. D., Köllner, F., Burkart, J., Bozem, H., Thomas, J. L.,Schneider, J., Aliabadi, A. A., Hoor, P. M., Schulz, H., Herber, A.B., and Leaitch, W. R.: Evidence for marine biogenic influenceon summertime Arctic aerosol, Geophys. Res. Lett., 44, 6460–6470, 2017.
14364 S. Kecorius et al.: New particle formation and its effect on CCN abundance in the summer Arctic
Willis, M. D., Leaitch, W. R., and Abbatt, J. P.: Processes control-ling the composition and abundance of Arctic aerosol, Rev. Geo-phys., 56, 621–671, 2018.
Yu, F.: Ion-mediated nucleation in the atmosphere: Key controllingparameters, implications, and look-up table, J. Geophys. Res.-Atmos., 115, D17205, https://doi.org/10.1029/2009JD012630,2010.
Zhang, W., Miller, P. A., Jansson, C., Samuelsson, P., Mao, J., andSmith, B.: Self-Amplifying Feedbacks Accelerate Greening andWarming of the Arctic, Geophys. Res. Lett., 45, 7102–7111,2018.
Zhou, J., Swietlicki, E., Berg, O. H., Aalto, P. P., Hämeri, K., Nils-son, E. D., and Leck, C.: Hygroscopic properties of aerosol par-ticles over the central Arctic Ocean during summer, J. Geophys.Res.-Atmos., 106, 32111–32123, 2001.
